An evolving subduction-related magmatic system in the Masara Gold District, Eastern Mindanao, Philippines

Abstract

The Masara Gold District in Eastern Mindanao, Philippines, is one of the most prolific gold provinces in the Philippines. Recent district-scale mineral exploration makes it possible to undertake geologic and geochemical studies and thus to yield better insights about the mineralization environment of the Masara Gold District.
In the Masara Gold District, mineralization is hosted in andesitic rocks and multiple stocks of diorite intrusions. New U-Pb and whole rock K-Ar age dating of these host rocks reveal Eocene to Plio-Pleistocene ages for the magmatic suites. A new lithologic unit is proposed to accommodate the composite diorite phases associated with mineralization. Major and trace element geochemistry of these host rocks show that the Eocene magmatic suite exhibits a tholeiitic character while the diorite and subvolcanic andesite pulses of the Miocene are calc-alkaline in composition. Adakitic rocks were emplaced during the Late Miocene and Plio-Pleistocene. Mineralization in eastern Mindanao is associated with several intrusive events formed during the Oligocene to the Pliocene. The majority of these mineralization events is associated with calc-alkaline magmatic suites. Based on this study, epithermal gold mineralization in the Masara Gold District is closely related to the Late Miocene magmatic rocks which exhibit calc-alkaline and adakitic signatures.

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Journal of Asian Earth Sciences: X
journal homepage: www.journals.elsevier.com/journal-of-asian-earth-sciences-x
An evolving subduction-related magmatic system in the Masara Gold
District, Eastern Mindanao, Philippines
Alfred Elmer Buena
a
, Barbie Ross B. Villaplaza
a
, Betchaida D. Payot
a
, Jillian Aira S. Gabo-Ratio
a
,
Noelynna T. Ramos
a
, Decibel V. Faustino-Eslava
b
, Karlo L. Queaño
c
, Carla B. Dimalanta
a,⁎
,
Jenielyn T. Padrones
d
, Kenichiro Tani
e
, Walter W. Brown
c
, Graciano P. Yumul Jr.
c
a
Rushurgent Working Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines
b
School of Environmental Science and Management, University of the Philippines, Los Baños, Laguna, Philippines
c
Apex Mining Company Inc., Ortigas Center, Pasig City, Metro Manila, Philippines
d
Institute of Renewable Natural Resources, College of Forestry and Natural Resources, University of the Philippines, Los Baños, Laguna, Philippines
e
Department of Geology and Paleontology, National Museum of Nature and Science, Tsukuba, Ibaraki, Japan
ARTICLE INFO
Keywords:
Gold-silver
Exploration potential
Epithermal mineralization
Magmatic host rocks
Masara
Mindanao
ABSTRACT
The Masara Gold District in Eastern Mindanao, Philippines, is one of the most prolific gold provinces in the
Philippines. Recent district-scale mineral exploration makes it possible to undertake geologic and geochemical
studies and thus to yield better insights about the mineralization environment of the Masara Gold District.
In the Masara Gold District, mineralization is hosted in andesitic rocks and multiple stocks of diorite intru-
sions. New U-Pb and whole rock K-Ar age dating of these host rocks reveal Eocene to Plio-Pleistocene ages for the
magmatic suites. A new lithologic unit is proposed to accommodate the composite diorite phases associated with
mineralization. Major and trace element geochemistry of these host rocks show that the Eocene magmatic suite
exhibits a tholeiitic character while the diorite and subvolcanic andesite pulses of the Miocene are calc-alkaline
in composition. Adakitic rocks were emplaced during the Late Miocene and Plio-Pleistocene. Mineralization in
eastern Mindanao is associated with several intrusive events formed during the Oligocene to the Pliocene. The
majority of these mineralization events is associated with calc-alkaline magmatic suites. Based on this study,
epithermal gold mineralization in the Masara Gold District is closely related to the Late Miocene magmatic rocks
which exhibit calc-alkaline and adakitic signatures.
1. Introduction
The Philippines forms part of the Cenozoic mineralized magmatic
systems bordering the Eurasian Plate in Southeast Asia and the northern
margin of the Australian continent in the western Pacific (e.g. Garwin
et al., 2005; Yumul et al., 2008). These magmatic systems are formed
from complex tectonic interactions with at least three major plate re-
organizations during the Tertiary (e.g. Hall, 1996, 2002). The geody-
namic framework makes this region prospective for hydrothermal gold-
copper mineralization. The region is well-endowed with world-class
copper-gold deposits such as Grasberg in Indonesia (MacDonald and
Arnold, 1994), the Porgera gold deposit and Ladolam gold mine, Lihir
Island, in Papua New Guinea (e.g. Moyle et al., 1990; Müller et al.,
2001; Ronacher et al., 2002), Hishikari in Japan (e.g. Garwin et al.,
2005) as well as the Lepanto and Dinkidi copper-gold deposits in the
Philippines (e.g. Claveria, 2001; Sillitoe and Hedenquist, 2003; Wolfe
and Cooke, 2011). The Philippines hosts at least six major gold districts
across the country: (1) the Baguio-Mankayan Gold District in Northern
Luzon; (2) the Paracale and (3) Masbate Gold Districts in Bicol; (4) the
Surigao and (5) Masara Gold Districts in Eastern Mindanao; and (6) the
Zamboanga Gold District in Western Mindanao (Fig. 1) (Mitchell and
Leach, 1991; Yumul et al., 2008).
The majority of these Philippine gold districts is well-constrained in
terms of their geology, geochemistry, geochronology and mineraliza-
tion type, respectively (e.g. Sajona et al., 2002; Payot et al., 2005;
Querubin and Yumul, 2005; Imai et al., 2009). However, studies on
epithermal gold mineralization in the Eastern Mindanao Gold-Copper
Province, which hosts the Masara Gold District, are rather limited be-
cause of its inaccessibility for political reasons in the past. Nonetheless,
recent developments gave rise to large-scale exploration campaigns
allowing to delineate its mineralization potential.
Since its discovery in 1937, the Masara Gold District has offered
https://doi.org/10.1016/j.jaesx.2019.100007
Received 14 April 2018; Received in revised form 7 January 2019; Accepted 10 January 2019
⁎
Corresponding author.
E-mail address: cbdimalanta@up.edu.ph (C.B. Dimalanta).
Journal of Asian Earth Sciences: X 1 (2019) 100007
Available online 28 January 2019
2590-0560/ © 2019 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
T

promising exploration potential for both porphyry copper and epi-
thermal gold deposits. However, systematic exploration work on the
district only commenced in 1975 which led to the discovery of por-
phyry copper prospects such as Kurayao and Teresa (Malihan et al.,
2015) located in the western portion of the study area (Fig. 2a). These
prospects have grades averaging 0.40% Cu and 0.40 g/t Au (Malihan
and Flores, 2012). At present, production and exploration is mainly
focused on the Masara Gold District epithermal veins with an estimated
total resource comprising 140 kt at 8.4 g/t Au using a 3 g/t Au cutoff
(Malihan and Flores, 2012).
Despite the long history of gold production in the area, there is still
a need to re-establish and refine the geology of the district based on the
recently accessible rock exposures. These studies are complemented
with the recent drillcore data and underground workings in order to
have a holistic approach in determining the geology and mineralization
of the area.
This paper integrates recent geologic, geochemical and geochrono-
logical data of the igneous rocks at the Masara Gold District.
Understanding the geology and geochemistry of this district and the
temporal sequence of host rock formation may contribute to elucidating
the tectonic evolution and magmatic history of the area. Results of this
study are also discussed in context with regional data on the tectonic
evolution of Eastern Mindanao. Discussing the link between tectonics
and metallogenesis of Eastern Mindanao may also provide an additional
understanding of the exploration potential of Cenozoic magmatic sys-
tems in the Southwest Pacific (e.g. Garwin et al., 2005; Zaw et al., 2014;
Basori et al., 2016; Gardiner et al., 2016; Qian et al., 2016).
2. Geologic background
2.1. Tectonic framework
Mindanao Island in the southern Philippines is bounded by two
different subduction systems. To the west, the Celebes Sea Plate and the
Sulu Sea Basin subduct beneath Mindanao and form the Cotabato and
Sulu-Negros Trench systems, respectively (Yumul et al., 2008; Aurelio
et al., 2013). The eastern portion of Mindanao is bounded by the sub-
duction of the Philippine Sea Plate along the Philippine Trench. There
are at least two major on-land sinistral faults that intersect the island
(Fig. 1): (1) the Sindangan-Cotabato-Daguma Lineament (SCDL) in the
south-central to northwestern portion; and (2) the southern extension
of the Philippine Fault Zone (PFZ) (e.g. Pubellier et al., 1991; Jimenez
et al., 2002; Yumul et al., 2008). The PFZ formed during the Pliocene
(Aurelio et al., 1991; Aurelio, 2000) and it is associated with the for-
mation of major copper and gold deposits across the country. The
principal gold districts such as Baguio-Mankayan, Paracale, Masbate,
Surigao and Masara are spatially related to this major structure. This
deep-seated lineament served as a conduit for metal-rich magmas and
hydrothermal fluids that formed these different gold districts in the
archipelago (Mitchell and Leach, 1991).
2.2. Geology of Eastern Mindanao
Eastern Mindanao is separated from Central Mindanao by the PFZ
(Fig. 1). Two dominant geomorphic terranes (Fig. 1) are observed in
Eastern Mindanao: the (1) Agusan – Davao Basin and (2) the Pacific
Cordillera (Pubellier et al., 1991). In Eastern Mindanao, the PFZ splits
into three N-NW trending sinistral splays named the Lianga and Cateel
Faults as well as the Pujada Thrust, which bound three microblocks of
the Pacific Cordillera (Malihan and Flores, 2012). These microblocks
belong to the Surigao District, the Central District and the Masara
District, respectively, which together comprise the Eastern Mindanao
Gold-Copper province. The province is bounded to the west by the main
shear of the PFZ (Mitchell and Leach, 1991) and it includes the Boy-
ongan-Bayugo porphyry copper deposit (Braxton and Mathur, 2011),
the sediment-hosted Siana gold deposit in the Surigao District, the Co-O
epithermal gold deposit in Agusan del Sur (Sonntag et al., 2011), the
Diwalwal epithermal gold deposit in the Central District as well as the
Masara epithermal gold and the Kingking porphyry copper deposits in
the Masara District (Suerte et al., 2009).
The region is underlain by Late Jurassic to Cretaceous basement
rocks consisting of meta-greenstones, greenschists and ophiolitic se-
quences. The ophiolitic sequences are unconformably overlain by vol-
cano-sedimentary units comprising basaltic and andesitic flows as well
as conglomerates, sandstones, limestones and shales, respectively.
These volcano-sedimentary suites occur throughout Eastern Mindanao
and are inferred to have been deposited during the Cretaceous to
Miocene period (Mitchell and Leach, 1991). Sajona et al. (1997) pro-
vide detailed work on the geochemistry and geochronology of the dif-
ferent rocks in Eastern Mindanao. Tholeiitic magmatism occurred
during the Eocene and produced andesitic lava flows throughout
Eastern Mindanao. These units are intruded by stock-like to batholitic
andesite porphyries and diorite plutons formed during the Oligocene to
Miocene period (e.g. Sajona et al., 1997; Pubellier et al., 1991). In
contrast to the Eocene tholeiitic magmatic rocks, the Oligo-Miocene
intrusions have calc-alkaline compositions (Sajona et al., 1997; Suerte
et al., 2009) and are spatially associated with the mineral deposits in
the region. The Oligocene Diwata Diorite is the only intrusion reported
at the Co-O epithermal gold deposit (e.g. Sonntag et al., 2011). At the
Kingking porphyry copper deposit, various calc-alkaline diorite
Fig. 1. Regional geologic map of Eastern Mindanao with the southern part of
the PFZ dividing the Pacific Cordillera and the Agusan-Davao Basin (after
Pubellier et al., 1991; Suerte et al., 2009). Locations with previously published
geochronological data are also shown (refer to Table 1). Inset shows the tec-
tonic setting of the Philippines showing the distribution of the six major gold
districts in the archipelago. 1 – Baguio-Mankayan, 2 – Paracale, 3 – Masbate, 4 –
Surigao, 5 – Masara and 6 – Zamboanga Gold Districts. The archipelago is
bounded by different subduction zone systems and intersected by the
∼1200 km-long Philippine Fault Zone (PFZ) as defined by PHIVOLCS (2016).
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
2

Fig. 2. (A) Geological map of the Masara Gold District showing the distribution of the rock units mapped. The NW- and EW-trending veins occur within the defined
mineralized zones. The porphyry copper prospects (e.g. Kurayao and Teresa) are found in the western portion of the study area. The locations of samples with
geochronological data are also shown. Please refer to Table 1 for the corresponding sample names. Inset shows the location of the Masara Gold District in Eastern
Mindanao. (B) Stratigraphic section of the Masara Gold District rock units showing the different stratigraphic relationships.
Fig. 3. Outcrops of the different rock units in the Masara Gold District. (A) The Alipao Andesite intruding the tuff unit of the Masara Formation found in the Calixto
area. (B) The Cateel Quartz Diorite intruding the andesite unit of the Masara Formation observed at Pjac. (C) Cliff-forming rocks of the Agtuuganon Limestone found
in the immediate north of the study area. The Agtuuganon Limestone unconformably overlies the Masara Formation. (D) Contact of the pyroclastic deposit of the
Amacan Volcanic Complex unconformably overlying the tuff of the Masara Formation basement rocks. (E–H) Outcrops of the Lamingag Intrusive Complex (LIC). (E)
The diorite porphyry unit of the LIC intruding the Masara Formation in Don Fernando. (F) Fritted and chilled contact between the LIC – diorite porphyry (LIC-DP) and
the Alipao Andesite (AA). (G) Aphyric andesite unit of the LIC in Calixto and (H) Equigranular diorite dikes near Pjac. (I) Epithermal vein on the ceiling of an
underground tunnel in the Masara Mine.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
3

intrusions occur as stocks and dikes and represent the host rocks of the
gold and copper mineralization (Suerte et al., 2009). A late-stage Plio-
Pleistocene subduction-related magmatic phase produced andesitic to
dacitic rocks that form the youngest volcanic units in the region (Sajona
et al., 1997).
The Masara Gold District is situated at the southern end of the
Pacific Cordillera at Maco, Compostela Valley in Eastern Mindanao. The
district is bounded by a NW-trending structural corridor associated with
the PFZ (Fig. 1;Mercado et al., 1987; Malihan and Flores, 2012). The
district mainly hosts porphyry copper (e.g. Kurayao and Teresa pro-
spects) and epithermal gold deposits (Masara epithermal gold) which
are currently exploited by Apex Mining Co., Inc. (AMCI). Minor oc-
currences of sediment-hosted and skarn deposits are also reported
(Malihan and Flores, 2012).
2.3. Geology of the Masara Gold District
The district consists of several geologic units: (1) the Masara
Formation which forms the basement that is unconformably overlain by
(2) the Agtuuganon Limestone. Both units are intruded by composite
stocks of, in order of decreasing age, (3) the Cateel Quartz Diorite, (4)
the plagiophyric Alipao Andesite, and (5) the late-stage Lamingag
Intrusive Complex (LIC) which is composed of fine-grained andesite,
diorite porphyry and quartz diorite stocks, respectively. All units are
unconformably overlain by (6) the Amacan Volcanic Complex, which
represents the youngest unit (Fig. 2b). Mineralization and associated
hydrothermal alteration are hosted by the units of the Masara Forma-
tion, the Cateel Quartz Diorite, the Alipao Andesite and the LIC, re-
spectively.
2.3.1. Masara Formation
The term Masara Formation was introduced by Malicdem and Peña
(1966) to describe the highly indurated wackestones with minor in-
tercalated calc-arenites and andesitic flows, flow breccias and pyr-
oclastic deposits. The Masara Formation forms the basement of the
area. The formation corresponds to the Eocene flows, tuffs and volcanic
wackestones described by Sajona et al. (1997). These units are wide-
spread in the Panuraon area, immediately to the north of the study area
(Fig. 1). An Eocene age (47.16 ± 1.50 Ma) is assigned to a lava flow
sample associated with the volcanic breccia collected at North Davao
using whole rock K-Ar dating (Sajona et al., 1997). In the study area,
exposures of the Masara Formation are best preserved in the Don Fer-
nando and Calixto areas as intercalated andesite flows or tuff deposits
(Fig. 3a). Exposures of this formation have a dark to reddish brown
color and are usually highly jointed with varying degrees of silicifica-
tion and chloritization. The andesite unit typically exhibits flow tex-
tures with a parallel alignment of plagioclase phenocrysts (0.3–0.7 mm)
that are set in a groundmass of plagioclase microlaths (Fig. 4a). The
lithic tuff deposits interconnected with the andesite flows contain la-
pilli-sized andesite clasts (Fig. 4b). The andesite and tuff samples from
this formation characteristically have high magnetic susceptibilities
(ranging from 3.67 to 34.2) and they are overprinted by a weak
chlorite-sericite alteration.
2.3.2. Agtuuganon Limestone
The Agtuuganon Limestone, previously referred to as the
Agtuuganon Formation (MMAJ-JICA, 1973), consists of coralline
limestones observed at Mt. Agtuuganon in the Compostela Valley,
Davao del Norte (Fig. 1). Based on foraminiferal assemblages in the
associated calcareous marls, the limestones formed during the Early to
Middle Miocene (Quebral, 1994). In the study area, the limestone unit
unconformably overlies the Masara Formation. Samples obtained from
this limestone unit exhibit a buff to light-grey appearance and they are
strongly silicified. Exposures of this formation are limited within the
study area. However, this unit is best preserved as cliff-forming rocks
immediately to the north of the study area (Fig. 3c).
2.3.3. Cateel Quartz Diorite
The Cateel Quartz Diorite was first described by Malicdem and Peña
(1966) to refer to the diorite stocks exposed in the Masara mine area.
The diorite intrusions can also be observed in the upper reaches of the
Caraga and Cateel Rivers (Fig. 1) in North Davao. In this study, units of
the Cateel Quartz Diorite are documented as stocks of quartz diorite
intruded into the Masara Formation (Fig. 3b). Exposures are wide-
spread throughout the study area and are best exposed at Pjac and
along the Causagisan Creek (Fig. 2a). This diorite body predominantly
Fig. 4. Representative photomicrographs of the different rock units (cross-ni-
cols). (A) Andesite flow of the Masara Formation exhibiting strong flow textures
primarily consisting of plagioclase (plag) phenocrysts that are set in a plagio-
clase rich-groundmass. The plagioclase phases are selectively altered to sericite
(ser). (B) Lapilli-sized lithic unit showing andesite clasts (and) derived from the
Masara Formation andesite flow. (C) Diorite stocks of the Cateel Quartz Diorite
are dominantly medium-grained consisting of plagioclase, hornblende (hbl) and
quartz (qtz). Plagioclase is usually altered to sericite. (D) The Alipao Andesite
exhibits plagioclase-rich phenocrysts that are set in a mafic groundmass.
Hornblende phenocrysts are also observed but to a lesser extent. The mafic
mineral-dominated groundmass is predominantly altered to uralite (url), epi-
dote (epd), chlorite (chl) and calcite (cal). (E–G) Photomicrographs of the
various phases of the Lamingag Intrusive Complex (LIC). (E) The diorite por-
phyry unit is mainly composed of plagioclase that is set in a strongly sericitized
groundmass. (F) The andesite unit is commonly massive and exhibits a pilo-
taxitic groundmass. Plagioclase and hornblende are the most common minerals.
(G) The equigranular diorite exhibits medium-grained plagioclase, quartz and
hornblende as the primary minerals. (H) Dacite mainly consists of plagioclase
and quartz with minor hornblende and biotite. The dacite units are fresh and
unaltered.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
4

occurs as grey to light grey massive blocks with notable argillization
along structures associated with gold mineralization. The diorite in-
trusions contain at least three major sets of joints (NW strike with a NE
dip, NW strike with a SW dip and NE strike with a NW dip) and are cut
by predominantly NW-trending faults. In the eastern portion, the in-
trusive unit follows a NW-trend parallel to the general direction of the
PFZ (Fig. 2a). The intrusion is reported to have formed during the Early
to Middle Miocene based on regional cross-cutting relations (Malicdem
and Peña, 1966).
The quartz diorite has a holocrystalline texture and it consists of
euhedral plagioclase, subhedral hornblende and anhedral quartz with
grain sizes ranging from 0.3–1.2 mm, 0.3–0.6 mm and ∼0.2 mm, re-
spectively (Fig. 4c). The quartz diorite units also form the host rocks of
the epithermal gold mineralization. Sericite selectively alters plagio-
clase phenocrysts along its crystal margins and cleavages. Hornblende
is usually replaced by chlorite and pyrite. Minor overprints of a regional
propylitic alteration (chlorite-dominated with minor epidote) are also
observed in the area.
2.3.4. Alipao Andesite
The term Alipao Andesite refers to the andesite plugs exposed in the
vicinity of the Alipao and Siana mines at Surigao del Norte (UNDP,
1987). At Masara, the Alipao Andesite consists of rare plagioclase-
phyric andesite dikes exposed mainly within the Calixto area (Fig. 2a).
The unit intruded both the Masara Formation and the Cateel Quartz
Diorite. The andesite yields an age of 13.0 ± 0.6 Ma (Middle Miocene),
based on K-Ar dating (UNDP, 1987). Exposures of this andesite have a
dark brown color similar to the Masara Formation but they are dis-
tinguished from the latter by coarse-grained plagioclase phenocrysts.
The outcrops are commonly strongly fractured. In places, this unit also
hosts epithermal gold mineralization. The rocks have holocrystalline
and porphyritic textures (Fig. 4d). The unit ranges from plagioclase-
dominated phenocrysts set in a groundmass comprising pilotaxitic eu-
hedral plagioclase laths and subhedral interstitial hornblende phases
(Fig. 4d) to both plagioclase- and hornblende-phyric types. The plagi-
oclase phenocrysts vary in size from 0.4 to 1.2 mm and are partially
replaced by calcite. The phenocrysts are set in a groundmass of plagi-
oclase microlaths and fibrous aggregates of secondary uralite. Horn-
blende phenocrysts are altered by an early-stage epidote alteration as-
semblage followed by a chlorite overprint. A late-stage calcite
alteration partially replaces both the hornblende and plagioclase phe-
nocrysts.
2.3.5. Lamingag Intrusive Complex (LIC) (new unit)
The Lamingag Intrusive Complex (LIC) is our proposed new name to
define the recently documented suite of magmatic rocks found in the
eastern portion of the study area. The LIC includes three intrusive units:
(1) the diorite porphyry, (2) a fine-grained andesite, and (3) equi-
granular diorite dikes. These units are best preserved within the
Lamingag Creek (7°21′52.5″N, 126°02′54.3″E), a NW-trending stream
subparallel to the Masara Fault Zone (MFZ) (Fig. 2a).
The diorite porphyry occurs as dikes cutting the Masara Formation
which are best exposed in the Don Fernando area (Fig. 3e). Quenched
and chilled contacts of the diorite porphyry with the Cateel Quartz
Diorite and the Alipao Andesite are only documented in drillcore
samples (Fig. 3f). These samples show a chilled margin in the diorite
porphyry unit and fritted margins in both the Alipao Andesite and the
Cateel Quartz Diorite. The diorite porphyry has porphyritic textures
with plagioclase as the dominant phenocryst phase set in a coarse-
grained and silicified groundmass. The phenocrysts usually range from
0.4 to 1.5 mm, while the groundmass ranges from 0.05 to 0.2 mm in
size (Fig. 4e). This unit also hosts epithermal gold mineralization both
at its hanging wall and foot wall, respectively. Samples collected along
the immediate wall rocks of mineralization show high degrees of ser-
icitization overprinting both the phenocrysts and the groundmass.
The fine-grained andesite unit is best observed in the Calixto area
Table 1
Summary of published and new geochronological data from our study. Published data on the ages of the different rocks in the region are also listed. Locations of these samples are shown in Fig. 1b.
No. Sample Name Locality Identification Description Age Method Reference
1 LMN JM0505
05 (LMN)
Masara Mine Laminga-g Intrusive Complex medium-grained quartz diorite 7.1 ± 0.2 Ma whole rock K-Ar This study
2 UCX JSBC 6415 06 (UCX) Masara Mine Laminga-g Intrusive Complex aphyric andesite 8.2 ± 0.5 Ma whole rock K-Ar This study
3 CAL BVNP 6415 9D (CAL) Masara Mine Alipao Andesite plagioclase-rich porphyritic andesite 14.2 ± 1.4 Ma whole rock K-Ar This study
4 KUR KLQ 510 01 (KUR) Masara Mine Cateel Quartz Diorite medium to coarse-grained quartz diorite 19.9 ± 1.4 Ma U-Pb (zircon – LA-ICPMS) This study
5 129907 (129) Masara Mine Cateel Quartz Diorite medium-grained quartz diorite 20.3 ± 0.6 Ma U-Pb (zircon – LA-ICPMS) This study
6 Q 90-21 Lake Leonard – dacite 0.31 ± 0.11 Ma whole rock K-Ar Sajona et al. (1997)
7 PH 92-16 WR Amacan – diorite 18.09 ± 0.54 Ma whole rock K-Ar Sajona et al. (1997)
8 PH 93-82 North Davao – diorite 32.27 ± 0.78 Ma whole rock K-Ar Sajona et al. (1997)
9 PH 92-75 North Davao – diorite 46.14 ± 1.12 Ma whole rock K-Ar Sajona et al. (1997)
10 PH 92-82 North Davao – andesite flow associated with volcanic breccia 47.1 ± 1.58 Ma whole rock K-Ar Sajona et al. (1997)
11 KKII-11-1A Kingking – biotite diorite porphyry 11.4 ± 0.7 Ma K-Ar (plagioclase) Suerte (2007)
12 A-17-1E Amacan – quartz hornblende diorite 27.0 ± 1.5 Ma K-Ar (plagioclase) Suerte (2007)
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
5

(7°22′37.3″N, 126°01′54.1″E) where it forms massive blocks (Fig. 3g)
with a regional weak propylitic or weak chlorite-sericite alteration. The
unit consists of fine- to medium-grained euhedral plagioclase laths with
pilotaxitic textures (Fig. 4f). Anhedral to subhedral fine-grained horn-
blende typically occurs along the interstices of the plagioclase laths.
The massive and equigranular diorite has a medium-grained texture
and forms small plugs and stocks in the Pjac area (Fig. 3h). In places,
the equigranular diorite grades into more fine-grained phases. Textu-
rally, this diorite body is comparable to the Cateel Quartz Diorite which
consists of euhedral plagioclase, subhedral hornblende and anhedral
quartz (Fig. 4g). The unit displays a minor sericite alteration and se-
lective chlorite replacements of hornblende.
This study documents this new intrusive complex as a series of
major stocks of diorite porphyry associated with rare andesite and
equigranular diorite dikes that are mainly found in the eastern portion
of the study area. The intrusive phases of this igneous complex re-
present a distinct unit based on geochronological data (Table 1) and
cross-cutting relationships.
2.3.6. Amacan Volcanic Complex
The Amacan Volcanic Complex was defined by MGB (2010) de-
scribing the dacitic units associated with the Leonard Kniassef volcano,
an active volcano in the Compostela Valley. Dacite dikes cutting pyr-
oclastic deposits (Fig. 3d) were emplaced during the Pleistocene
(0.31 Ma) based on whole rock K-Ar dating by Sajona et al. (1997).
Malihan and Flores (2012), however, note that the dacite rocks in the
study area were formed during the Plio-Pleistocene based on strati-
graphic correlations. The latest activity associated with this dacitic
volcanism occurred at about 1.8Ka based on a
14
C age obtained from a
charred piece of wood hosted by the pyroclastic deposits (Barnett,
1983). Exposures of this formation are found in the vicinity of Lake
Leonard near the Teresa and Lumanggang tailings dam areas (Fig. 3d).
The unit usually has a light to dark grey colour. The pyroclastic com-
ponent of this complex unconformably overlies the Masara Formation
basement. The unit typically has porphyritic textures comprising phe-
nocrysts of fragmental plagioclase, brown euhedral hornblende and
biotite and subhedral to euhedral quartz. The phenocrysts usually have
medium-grained sizes (∼0.03 mm to 0.06 mm) and they are set in a
plagioclase- and quartz-rich groundmass (Fig. 4h). This unit post-dates
the epithermal gold mineralization and it is fresh and unaltered.
2.4. Structures
The Masara Gold District is intersected by the major NW-trending
Masara Fault Zone (MFZ) exposed in the eastern portion of the study
area (Malicdem and Peña, 1966) (Fig. 2a). The MFZ runs parallel to the
southern extension of the NW-trending Philippine Fault Zone. Surface
and underground structures of the MFZ show an oblique sinistral strike-
slip displacement with a transpressional component (Malicdem and
Peña, 1966). The MFZ hosts a series of steep NE-dipping mineralized
faults which are associated with bonanza-grade gold deposits at Ma-
sara. The bonanza-grade deposits are usually characterized by massive
chalcopyrite and pyrite-rich quartz veins following a NW trend. The
veins are usually 1 to 1.5 m wide and commonly thin out with depth.
Swarms of the NW-trending faults extend beyond the study area to-
wards the north and south, respectively. The mineralized structures
have an estimated strike length of at least 4 km. Several diorite units in
the eastern part of the area have a NW-trending distribution subparallel
to the MFZ. Second order EW fault systems with related WNW and ENE
Riedel trends with different dip directions form part of the main MFZ.
The epithermal gold veins in the district range from massive sulfide
through quartz-sulfide to quartz-carbonate veins which appear to re-
present low- to intermediate-sulfidation systems based on their textures
and sulfide assemblages (Fig. 3i).
3. Methodology
Representative rock units were selected for petrographic analyses.
Vein samples were also collected from the underground workings. Thin
sections at 30-µm thickness were prepared from the samples using the
Pelcon Automatic Thin Section Machine housed at the University of the
Philippines – National Institute of Geological Sciences (UP-NIGS). Thin
sections were polished with 1-µm diamond during the final polishing
stage. Petrographic analyses were conducted using the Olympus BX53-P
Polarizing Microscope at UP-NIGS. Mineralogical and textural char-
acteristics of the samples are documented.
Three relatively fresh host rocks from different lithologic units were
sent to Geochronex Analytical Services and Consulting in Ontario,
Canada, for whole rock K-Ar dating. For Ar analysis, an aliquot of each
sample was heated at ∼100 °C for 2 days in order to remove the surface
gases. Argon is extracted from the sample in a double vacuum furnace
at 1700 °C. Argon concentration is determined using isotope dilution
with an
38
Ar spike, which is introduced into the sample system prior to
each extraction. The extracted gases are cleaned in a two-step pur-
ification system. The purified Ar is introduced into the custom-built
magnetic sector mass spectrometer (Reynolds type) with a Varian CH5
magnet. Measurements of Ar isotope ratios are corrected for mass-dis-
crimination and subsequently atmospheric argon is removed based on
the assumption that
36
Ar is only derived from the air. Concentrations of
radiogenic
40
Ar are calculated from the
38
Ar spike concentration. The
extraction temperature is increased to 1800 °C for a few minutes and
the furnace is then prepared for the next analysis. For K-analyses, an
aliquot of the sample is weighed in the graphite crucible with lithium
metaborate/tetraborate flux and fused using the LECO induction fur-
nace. The fusion bead is dissolved with acid. Standards, blanks and
sample material are analyzed with the ICP mass spectrometer. Further
details on the theory and methodology conducted for K-Ar dating are
provided by Dickin (1995).
Two samples of the diorite were sent for U-Pb dating to the
Department of Geology and Paleontology, National Museum of Nature
and Science, Japan. Zircon grains were handpicked from heavy mineral
separates of the quartz diorite. The grains were mounted on epoxy resin
and were polished until the embedded grains were flattened. The
mounted grains were subjected to backscattered and cathode lumines-
cence imaging in order to select representative sites for zircon dating.
The quadrupole ICP-MS for U-Pb analysis was an Agilent 7700 × and
an ESI NWR213 laser ablation system. A Nd-YAG laser with a 213 nm
wavelength and 5 ns pulse was used for the analyses. Details of this
methodology are discussed by Tsutsumi et al. (2012). The Isoplot v. 3.7
program (Ludwig, 2008) was used for the Tera-Wasserburg concordia
plots and weighted average calculation, respectively.
Only representative rock units that are either fresh or very weakly
altered were selected for geochemical analyses. Samples from the dif-
ferent units were crushed and powdered at UP-NIGS using an agate
mortar and a pestle. Powdered samples were sent to Bureau Veritas
Commodities Canada Ltd. for major, trace and rare earth element
analyses using ICP-ES and ICP-MS equipment. Selected samples were
analyzed by X-Ray Fluorescence (XRF) at Kyushu University, Japan,
using the method discussed by Soejima (1999).
4. Results
4.1. Geochronological data
Whole rock K – Ar data and U – Pb zircon age dating results of the
host rocks of the Masara Gold District are summarized in Table 1.
Previously published geochronological data from the region (Sajona
et al., 1997; Suerte, 2007) are also incorporated in Table 1 with their
respective locations plotted on Fig. 1.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
6

4.1.1. K–Ar dating
LMN JM0505 05 (LMN). The sample was collected from the
Lamingag Creek (7°21′52.5″N, 126°02′54.3″E). The rock is a medium-
grained equigranular and holocrystalline quartz diorite composed of
subhedral to euhedral hornblende, plagioclase and anhedral quartz. It
belongs to the Lamingag Intrusive Complex (LIC). The sample yields a
whole-rock age of 7.1 ± 0.2 Ma (Late Miocene).
UCX JSBC 6415 06 (UCX). The sample was collected in the Upper
Calixto area (7°22′37.3″N, 126°01′54.1″E). The rock forms a massive
aphyric andesite that is part of the LIC. Petrographic analysis of the
sample reveals fine-grained euhedral plagioclase with very fine-grained
subhedral interstitial hornblende phases. The plagioclase laths have a
pilotaxitic texture. The sample is dated at 8.2 ± 0.5 Ma (Late
Miocene).
CAL BVNP 6415 9D (CAL). The sample was also collected from the
Calixto area, but in the central portion of the AMCI mining tenement
(7°22′52.2″N, 126°01′46.5″E). The rock is a porphyritic andesite con-
taining abundant fine- to medium-grained euhedral plagioclase phe-
nocrysts and it forms part of the Alipao Andesite. Phases of this unit
intrude the tuffs of the Masara Formation. The sample is dated at
14.2 ± 1.4 Ma (Middle Miocene).
4.1.2. U–Pb zircon dating
KUR KLQ 510 01 (KUR). This sample was taken from the Kurayao
area to the west of the AMCI mining tenement (7°23′1.5″N,
126°01′22.1″E). The rock belongs to the widely exposed Cateel Quartz
Diorite. It has a massive and equigranular texture composed of medium-
to coarse-grained euhedral plagioclase, subhedral hornblende and
minor anhedral quartz.
129907 (129). This is a drillcore sample from the Sandy area in the
east (7°21′58.3″N, 126°02′49.1″E). The rock has holocrystalline and
equigranular textures consisting of medium- to coarse-grained euhedral
plagioclase, subhedral hornblende and minor anhedral quartz. The rock
belongs to the mapped Cateel Quartz Diorite.
Zircon grains range from subhedral to euhedral in shape with
equant, tabular, and prismatic habits. The cathodoluminescence images
show oscillatory and sector zoning in zircon grains from both samples
(Fig. 5a). Result from KUR sample’s
238
U/
206
Pb
(2)
ages range from 13.2
to 22.1 Ma (Table 2). The weighted mean
207
Pb- corrected
238
U/
206
Pb
age of the zircons derived from this sample provide an age of
19.9 ± 1.4 Ma (Early Miocene) whereas the Terra-Wasserburg con-
cordia plot shows concordant ages at 19.0 ± 2.6 Ma age intercept
(Fig. 5b). The
238
U/
206
Pb
(2)
ages of sample 129,907 range from 18.9 to
22.2 Ma (Table 2). The weighted mean
207
Pb- corrected
238
U/
206
Pb age
is at 20.3 ± 0.59 Ma (Early Miocene). On the other hand, the Terra-
Wasserburg concordia plot shows age intercept at 20.39 ± 0.65 Ma
(Fig. 5c).
4.2. Whole-rock geochemistry
Major and trace element compositions of representative rock units
are summarized in Table 3. Samples with geochronological results are
plotted as shaded symbols (Figs. 6 and 7). On the Zr/TiO
2
vs. Nb/Y
diagram of Winchester and Floyd (1977), the rocks of the Masara
Formation and the Alipao Andesite plot in the andesite/basalt field
(Fig. 6a). Samples from the Cateel Quartz Diorite mainly plot in the
andesitic field while two samples fall into the rhyolite field. Units of the
Lamingag Intrusive Complex and the Amacan Volcanic Complex com-
monly fall between the rhyodacite/dacite and andesite fields, respec-
tively (Fig. 6a). When applying the Zr-Nb-Th tectonic discrimination
diagram of Wood (1980), all of these units plot in the arc-basalt field
(Fig. 6b). The diagram of Miyashiro (1974) using FeO/MgO vs. SiO
2
and the AFM diagram of Irvine and Baragar (1971) were used in order
to discriminate between tholeiitic and calc-alkaline compositions of
these units (Fig. 6c and d). On both diagrams, the Masara Formation
plots in the tholeiitic field while samples from the Cateel Quartz Diorite,
Alipao Andesite, Lamingag Intrusive Complex and the Amacan Volcanic
Complex fall within the calc-alkaline field. Trace element compositions
normalized to MORB (Pearce et al., 1984) show very weakly enriched
LILE for the Masara Formation, but more pronounced LILE enrichments
of the Cateel Quartz Diorite, the Alipao Andesite, the Lamingag In-
trusive Complex and the Amacan Volcanic Complex, respectively. All
these rock units exhibit strongly pronounced negative Nb, Ta and Ti
anomalies and a slightly pronounced Zr negative anomaly (Fig. 7),
which are typical features of subduction-related magmas (Saunders
et al., 1980; Briqueu et al., 1984).
Harker diagrams show that with increasing SiO
2
contents (pro-
ceeding fractionation), the oxides Al
2
O
3
, FeO, MgO, CaO, TiO
2
and
P
2
O
5
decrease. However, this correlation is less obvious when plotting
K
2
O and Na
2
O vs. SiO
2
(Fig. 8).
5. Discussion
5.1. Tertiary magmatism in the Masara Gold District
This study reports new K-Ar and U-Pb zircon ages of the different
rock units of the Masara Gold District. The new age data and the results
from new whole-rock geochemical analyses in context with previously
published data from the region (e.g. Sajona et al., 1997; Suerte, 2007;
Sonntag et al., 2011), are used to provide a better understanding of the
magmatic history and tectonic setting of the Masara Gold District.
Geochronological data from this study also reveal a new and distinct
lithologic unit, the Lamingag Intrusive Complex, which adds to the
stratigraphy of the Masara Gold District (Fig. 2a).
Magmatism in the Masara Gold District occurred from the Eocene to
the Plio-Pleistocene comprising andesitic flows and associated tuffs,
composite diorite stocks, porphyritic andesites, andesite dikes and a
late-stage dacite lava. An Eocene age was suggested by Sajona et al.
(1997) for the andesite flows of the Masara Formation described in this
study. The Masara Formation is intruded by the Cateel Quartz Diorite
which has previously been assigned an Early to Middle Miocene age
based on stratigraphic correlations (Malicdem and Peña, 1966). This
study, however, reveals a more precise weighted mean
207
Pb corrected
206
Pb/
238
U zircon age from two samples of the Cateel Quartz Diorite
dated at 19.9 ± 1.4 and 20.3 ± 0.6 Ma (Early Miocene). The por-
phyritic Alipao Andesite dike intersecting these rocks is dated at
14.2 ± 1.4 Ma (Middle Miocene) using whole-rock K-Ar methods. This
is comparable to the previously published whole-rock K-Ar ages of
UNDP (1987) yielding about 13.0 ± 0.6 Ma (Middle Miocene). Sub-
sequent phases of andesite and diorite porphyry dikes cut the Alipao
Andesite, the Cateel Quartz Diorite and the Masara Formation. These
units constitute the newly proposed lithologic unit of the Masara Gold
District, the Lamingag Intrusive Complex (LIC). Whole-rock K-Ar dating
reveals ages of 8.2 ± 0.5 Ma (Late Miocene) for the andesite dikes and
7.1 ± 0.2 Ma (Late Miocene) for the small diorite bodies. The diorite
porphyry formed during the Late Miocene as suggested by cross-cutting
relationships with the Middle Miocene Alipao Andesite (Fig. 3f).
On MORB-normalized multi-element diagrams, the igneous rocks of
the Masara Gold District show island arc signatures that also explain the
distinctly negative Nb, Ta, Zr and Ti anomalies (Fig. 7). The geo-
chemical signatures are similar to the magmatic rocks of Eastern
Mindanao (Sajona et al., 1997; Suerte et al., 2009; Sonntag et al., 2011)
(Fig. 7). This arc signature is further supported by the Zr-Nb-Th dis-
crimination diagram (Wood, 1980) with all samples plotting in the arc-
basalt field (Fig. 6b).
The Harker diagrams of the different rocks in the Masara Gold
District show a decrease in Al
2
O
3
, FeO, MgO, CaO, TiO
2
and P
2
O
5
with
increasing SiO
2
contents (Fig. 8). This general trend may be attributed
to fractional crystallization of plagioclase, amphibole, apatite and
magnetite, but may also be due to the varying melt conditions in the
magma source through time. Although fractionation may be the
dominant process involved in the Masara Gold District, the role of
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
7

assimilation and magma mixing are not totally discounted.
The Masara Formation forms part of the wide-spread tholeiitic arc
magmatism during the Eocene in Bicol, Leyte, Central and Eastern
Mindanao (Sajona et al., 1997). This magmatism extends all the way to
the Oligocene as manifested by the dated tholeiitic diorite samples from
North Davao by Sajona et al. (1997).Suerte et al. (2009), however,
reported Oligocene intrusions with calc-alkaline compositions at
Kingking (Fig. 6c and d). This calc-alkaline suite is also quite common
in the Co-O District (Sonntag et al., 2011).
The occurrence of both tholeiitic and calc-alkaline Oligocene rocks
in Eastern Mindanao (Fig. 6c and d) marks the geochemical transition
from an initial Eocene island arc towards a more mature calc-alkaline
island arc during the Oligocene to Miocene (Sonntag et al., 2011). The
spatio-temporal relationships between the tholeiitic and calc-alkaline
magmatic suites has already been established in other magmatic arcs
worldwide (e.g. Hunter and Blake, 1995; Macdonald et al., 2000). Al-
though Oligocene rocks are not recorded in the described area, the
study of Sonntag et al. (2011) documents such units at Co-O, to the
north of our study area. Geochemical data from these Oligocene units
reveal both tholeiitic and calc-alkaline features (Fig. 6d). Hence, this
Fig. 5. (A) Representative cathodoluminescence images of zircon samples from the quartz diorite at Cateel. Red circles show the analyzed spots while numbers refer
to the analyses shown in Table 2. Concordia plots and weighted mean average diagrams for zircons from (B) KUR and (129907) samples. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of this article.)
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
8

study further infers that the transition from tholeiitic to calc-alkaline
magmatism occurred during the Oligocene as previously suggested by
Sonntag et al. (2011).
In our study, the Eocene tholeiitic rocks of the Masara Formation
show very weak enrichments in LILE while the Early Miocene calc-al-
kaline Cateel Quartz Diorite has a more pronounced enrichment in
these elements. Both of these units exhibit island arc signatures (Fig. 6b
and 7). The younger magmatic suites such as the Alipao Andesite, the
Lamingag Intrusive Complex and the Amacan Volcanic Complex are
also characterized by enriched LILE and island arc signatures. These
general similarities in the geochemistry and tectonic setting of the
magmatic rocks in Eastern Mindanao confirm previously published
studies (e.g. Sajona et al., 1997; Suerte et al., 2009; Sonntag et al.,
2011).
Adakitic magmatism has also been documented in the Philippines in
Eastern Mindanao, especially during the Pliocene (Sajona et al., 1997;
Macpherson et al., 2006). Adakite was initially used as a genetic term to
describe the partial melting of Cenozoic silicic magmas derived from a
relatively young subducted slab (< 25 Ma) (Defant and Drummond,
1990). Different models have been proposed to elucidate the origin of
intermediate-felsic adakitic rocks (e.g. Martin et al., 2005; Castillo,
2012; Ma et al., 2016). Various mechanisms of adakite formation in-
clude lower crust melting, slab melt-mantle interaction and high pres-
sure fractionation, etc. (e.g. Jego et al., 2005; Wang et al., 2006;
Chiaradia, 2015).
More recently, Yumul et al. (2017) report adakitic signatures of the
Plio-Pleistocene Amacan Volcanic Complex in the Masara Gold District.
Based on Dy/Yb ratios vs. SiO
2
plots and the U-shaped concave upward
REE spidergram pattern of these rocks, their genesis was assigned to the
fractional crystallization of amphiboles. Yumul et al. (2017) also
documents adakitic compositions in the Late Miocene Lamingag In-
trusive Complex. In contrast to what was previously suggested by
Sajona et al. (1997), this suggests that adakitic magmatism started
earlier than about 4.5 Ma. Yumul et al. (2017) also demonstrate that the
adakitic rocks in the Masara Gold District are not necessarily associated
with mineralization. This is contrary to what Sajona and Maury (1998)
suggested linking adakitic magmatism to mineralization in Eastern
Mindanao.
5.2. Tectonic history
Magmatism in the Masara Gold District occurred during the Eocene
to the Pleistocene. The Eocene tholeiitic Masara Formation forms the
basement rocks in the study area. This Eocene magmatism is attributed
to subduction processes, possibly related to an intra-oceanic arc outside
the proto-Philippine Sea Plate (Fig. 9a and b). A possible locus of this
magmatism is the proto-Molucca Sea Plate, which constitutes a lost
microplate proposed to fill the tectonic gaps in reconstructing the plate
tectonics of Southeast Asia during the Cenozoic (e.g. Sajona et al., 1997;
Rangin et al., 1999; Wu et al., 2016). The existence of the proto-Mo-
lucca Sea Plate during the Cenozoic is indicated by seismic tomography
studies by Zahirovic et al. (2014). Their work suggests a northeast-
dipping subduction of the proto-Molucca Sea Plate, in contrast to the
westward-subduction proposed earlier by Sajona et al. (1997). In our
study, the new model of Zahirovic et al. (2014) is adopted due to their
detailed and comprehensive compilation of geological and geophysical
parameters (see also: Lee and Lawver, 1995; Hall, 2012; Seton et al.,
2012).
Subsequent magmatic activity formed the calc-alkaline stocks of the
Cateel Quartz Diorite during the Early Miocene (Fig. 9c). The magma-
tism waned during the beginning of the Early Miocene to the Middle
Miocene (Sajona et al., 1997), probably due to the collision of a paleo-
island arc with Eastern Mindanao. The southern portion of this paleo-
arc is preserved as the Snellius Plateau (Mitchell et al., 1986). The
Cretaceous to Eocene rocks of the Pacific Cordillera probably represent
the upper part of the Snellius Plateau (Pubellier et al., 1999).
In the Masara area, this weak magmatic period is represented by the
plagioclase-phyric andesite dikes of the Middle Miocene Alipao
Table 2
U-Pb data of zircons from the Cateel Quartz Diorite.
Labels
206
Pb
c1
(%) U (ppm) Th (ppm) Th/U
238
U/
206
Pb*
1207
Pb*/
206
Pb*
1238
U/
206
Pb* age
1
(Ma)
238
U/
206
Pb* age
2
(Ma)
KUR-1 8.39 54 13 0.24 325.16 ± 37.29 0.0722 ± 0.0662 19.8 ± 2.3 19.2 ± 2.3
KUR-2 0.69 87 25 0.29 306.39 ± 25.48 0.1296 ± 0.0404 21.0 ± 1.7 18.8 ± 1.8
KUR-3 0.00 70 19 0.28 303.77 ± 27.65 0.0908 ± 0.0287 21.2 ± 1.9 20.0 ± 2.0
KUR-4 0.00 101 31 0.32 326.75 ± 24.97 0.0548 ± 0.0261 19.7 ± 1.5 19.5 ± 1.6
KUR-5 12.40 69 24 0.35 461.65 ± 49.27 0.0908 ± 0.0777 13.9 ± 1.5 13.2 ± 1.5
KUR-6 0.00 123 67 0.56 378.72 ± 25.04 0.0274 ± 0.0231 17.0 ± 1.1 17.0 ± 1.1
KUR-7 0.38 58 18 0.33 269.65 ± 25.84 0.1557 ± 0.0492 23.9 ± 2.3 20.6 ± 2.2
KUR-8 0.00 107 33 0.32 287.94 ± 16.49 0.0576 ± 0.0219 22.3 ± 1.3 22.0 ± 1.4
KUR-9 1.83 83 24 0.29 282.37 ± 25.44 0.0706 ± 0.0505 22.8 ± 2.0 22.1 ± 2.0
KUR-10 0.00 107 34 0.33 299.63 ± 18.38 0.0406 ± 0.0181 21.5 ± 1.3 21.5 ± 1.3
KUR-11 0.00 105 61 0.59 308.71 ± 22.44 0.0380 ± 0.0232 20.8 ± 1.5 20.8 ± 1.5
129907-1 0.10 469 514 1.12 307.57 ± 12.85 0.0253 ± 0.0153 20.9 ± 0.9 20.9 ± 0.8
129907-2 0.00 342 170 0.51 340.75 ± 17.17 0.0474 ± 0.0083 18.9 ± 1.0 18.9 ± 1.0
129907-3 0.00 254 164 0.66 307.21 ± 14.16 0.0176 ± 0.0085 20.9 ± 1.0 20.9 ± 1.0
129907-4 0.56 364 262 0.74 312.19 ± 12.42 0.0249 ± 0.0142 20.6 ± 0.8 20.7 ± 0.8
129907-5 1.50 353 178 0.52 295.73 ± 10.96 0.0337 ± 0.0146 21.8 ± 0.8 22.1 ± 0.8
129907-6 0.00 280 119 0.44 283.18 ± 12.03 0.0654 ± 0.0094 22.7 ± 1.0 22.2 ± 1.0
129907-7 0.00 222 128 0.59 298.79 ± 15.45 0.0523 ± 0.0112 21.5 ± 1.1 21.4 ± 1.1
129907-8 0.00 269 134 0.51 314.58 ± 15.44 0.0437 ± 0.0109 20.5 ± 1.0 20.5 ± 1.0
129907-9 0.00 564 428 0.78 329.82 ± 11.00 0.0494 ± 0.0062 19.5 ± 0.6 19.4 ± 0.7
129907-10 0.13 440 297 0.69 312.72 ± 12.18 0.0590 ± 0.0134 20.6 ± 0.8 20.3 ± 0.8
129907-11 0.53 453 395 0.90 323.44 ± 11.19 0.0523 ± 0.0156 19.9 ± 0.7 19.8 ± 0.6
129907-12 11.17 807 681 0.87 325.37 ± 10.52 0.0265 ± 0.0186 19.8 ± 0.6 20.3 ± 0.6
129907-13 5.28 517 369 0.73 345.22 ± 11.14 0.0224 ± 0.0154 18.6 ± 0.6 19.2 ± 0.6
Errors are 1-sigma; Pb
c
and Pb* indicate the common and radiogenic portions, respectively.
1
Common Pb corrected by assuming
206
Pb/
238
U-
208
Pb/
232
Th age-concordance.
2
Common Pb corrected by assuming
206
Pb/
238
U-
207
Pb/
235
U age-concordance.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
9

Table 3
Major oxide and trace element compositions of representative magmatic rocks of the Masara Gold District expressed in wt.% and ppm, respectively. b.d.l. – below detection limit. Standard of error for major oxides are at
1% for ICP-ES/MS and the XRF accuracy is within 0.03%. Standard of error for trace elements are at 5% for ICP-ES/MS and the XRF accuracy is within 0.001%.
Sample Name PAG-RJM-
0515-11
BC-KEL-501-6 OFW-NPJG-
0510-18
NUR MCEB
6615-2A
TER-BRV-
6415-7B
DFW-NPJG-
0510-11
APEX-
129923
KUR-KLQ-
0510-01
KURKIT-
0512-01
PAG-KEL
0513-8
129912 TER 60215
RECON-1
TERBRV6415-7A SFS JGGV
6516-6
CAL-BVNP-060515-9D Rock ID Masara Fm.
andesite
Masara Fm.
andesite
Masara Fm.
andesite
Masara Fm.
andesite
Masara Fm.
andesite
Cateel Qtz.
Diorite
Cateel Qtz.
Diorite
Cateel Qtz.
Diorite
Cateel Qtz.
Diorite
Cateel Qtz.
Diorite
Alipao
Andesite
Alipao Andesite Alipao
Andesite
Alipao Andesite Alipao
Andesite
wt.%
SiO
2
51.79 59.56 44.07 54.44 51.35 63.51 54.8 65.65 72.35 57.34 56.23 59.72 59.87 55.07
54.4 Al
2
O
3
15.52 16.18 21.17 16.8 19.87 16.02 17.66 14.81 8.72 19.11 15.88 13.8 16.99
16.38 16.86
Fe
2
O
3
13.23 6.24 15.49 10.38 12.2 7.45 7.25 4.58 8.7 6.79 6.43 10.18 6.06 9.14
9.5 MgO 4.44 2.01 3.42 5.48 2.43 1.89 2.92 1.56 2.4 3.5 5.52 5.52 2.98
5.28 3.3
CaO 5.41 4.84 3.32 6.86 1.93 1.17 6.81 1.94 0.33 0.17 6.67 3.9 4.69 9.23
7.65 Na
2
O 2.58 4.22 3.48 3.56 3.79 3.37 3.84 1.71 2.28 0.47 4.2 2.57 4.09
2.26 3.28
K
2
O 0.3 1.66 1.25 0.27 1.6 1.99 1.35 5.86 0.18 3.14 2.22 0.31 1.01 0.3
0.88 TiO
2
1.13 0.43 1.2 1.02 1.25 0.37 0.69 0.34 0.3 1.06 0.58 0.58 0.47
0.81 0.96
P
2
O
5
0.27 0.16 0.24 0.31 0.1 0.15 0.23 0.14 0.06 0.36 0.19 0.24 0.21 0.28
0.26 LOI 4.7 4.3 5.9 0.42 5.1 3.3 3.9 2.5 3.6 7.8 1.5 2.07 3.29
0.76 2.5
Sum 99.56 99.79 99.58 99.53 99.66 99.34 99.79 99.44 99.03 99.8 99.71 98.91 99.67 99.5
99.73
ppm
Ba 40 630 117 43 245 249 357 1054 13 487 432 38 100 116
369 Hf 1.9 2.3 2.3 2.3 2.5 2.3 1.7 2.2 1.4 3.1 2.4 1.7 2.4
2.2 2.7
Nb 2 2.3 1.9 1.9 2 2.1 1.8 3.1 0.9 2.7 4.1 2.8 2.6 1.9
1.7 Rb 7.3 22.1 30.2 3.5 28.2 44.8 26.1 122 3.7 50.2 40.4 3.1 14.9
3.3 14.3
Sr 269 434.7 299 292.5 243.5 182.4 386.2 279 66.8 31.8 826.7 154.2 113.5 353.5
402.9 Ta 0.2 0.2 0.1 b.d.l. b.d.l. 0.2 0.1 0.2 0.1 0.3 0.4 b.d.l. 0.3
0.1 0.1
Th 0.8 1.5 0.6 b.d.l. b.d.l. 1.5 0.9 1.7 0.6 1.3 1.9 b.d.l. b.d.l. b.d.l.
b.d.l. Zr 70.1 84.9 73.1 82.7 80.2 87.6 54.6 85.4 50.6 108.4 88.8 59.3 83.7
73.5 89.3
Y 19.5 14.6 23.2 24.9 18.5 13.1 18 12 16.9 15.6 11.9 21.8 16.9 21.3
21.6 Ce 20.9 15.7 16.5 20.6 19.6 8.7 15.7 17.5 7.1 15.5 20.6 12.7 16
17.8 18.2
Sm 3.54 2.05 3.47 4.29 3.59 1.39 2.62 1.95 1.61 3.6 2.56 3 1.98 2.82
3.2 Yb 2.2 1.68 2.42 2.51 2.26 1.46 1.86 1.36 1.46 1.89 1.14 2.14 1.62
2.22 2.23
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
10

Andesite. The formation of the biohermal Agtuuganon Limestone
during the Early to Middle Miocene also implies a period of quiescence
in magmatic activity (Fig. 9d). In the Late Miocene, the onset of the
eastward subduction of the Molucca Sea Plate beneath the Halmahera
trench resulted in the reactivation of magmatic activity in the area
(Sufni Hakim and Hall, 1991) (Fig. 9e). In the study area, this period is
possibly reflected by the Late Miocene intrusive rocks of the Lamingag
Intrusive Complex.
The major NW-trending Masara Fault Zone (MFZ) forms a magmatic
plumbing system transecting the study area, and the Early Miocene
Cateel Quartz Diorite is emplaced along this structural corridor.
Additionally, the major epithermal gold veins in the Masara Gold
District are also oriented subparallel to the MFZ. Recent geochronolo-
gical data from the Cateel Quartz Diorite implies that the MFZ pre-dates
the Pliocene PFZ. Hence, the MFZ has existed at least since the Early
Miocene. Quebral (1996) record two distinct styles of neotectonic de-
formation in Eastern Mindanao: (1) an older set of compressive struc-
tures distributed over a wide area and (2) an active left-lateral strike
slip fault system. This left-lateral strike-slip fault system corresponds to
the PFZ which probably reactivated pre-existing collision-related
structures (Quebral, 1996). In the Masara area, the MFZ was reactivated
by the formation of the PFZ, which subsequently served as a conduit for
mineralizing hydrothermal fluids to precipitate the epithermal gold
veins.
A Plio-Pleistocene adakitic magmatic phase formed the younger
volcanic units in the region (Fig. 9f). In the study area, the Plio-Pleis-
tocene dacitic Amacan Volcanic Complex is attributed to the eruption of
the Leonard Kniassef volcano, the only active volcano in the southern
portion of Eastern Mindanao. A recent study by Yumul et al. (2017)
proposes that these Plio-Pleistocene adakitic rocks are products of
amphibole fractionation.
5.3. Relationship to gold mineralization
Epithermal gold mineralization is commonly associated with calc-
alkaline and/or alkaline magmatism derived from fractionated melts in
subduction settings (e.g. Sillitoe, 1997; Cooke and Simmons, 2000;
Hollings et al., 2011; Waters et al., 2011). At Masara, gold miner-
alization is associated with the late-stage intrusive phases of the calc-
alkaline Lamingag Intrusive Complex. To the south of the study area,
Fig. 6. (A) Zr/TiO
2
vs. Nb/Y diagram (Winchester and Floyd, 1977) showing the different compositions of the Masara Gold District rock units ranging from andesite/
basalt to andesite-dacite compositions. (B) Samples plot in the arc-basalt field of the Zr-Th-Nb diagram (Wood, 1980). (C) FeO/MgO vs. SiO
2
diagram after Miyashiro
(1974) discriminating tholeiitic and calc-alkaline compositions of the rocks of Masara Gold District as well as regional geochemical data. (D) AFM Diagram (Irvine
and Baragar, 1971) assigning a tholeiitic composition to the Masara Formation and a calc-alkaline signature to the Cateel Quartz Diorite, the Alipao Andesite, the
Lamingag Intrusive Complex and the Amacan Volcanic Complex, respectively. Available regional geochemical data are also shown (e.g.Sajona et al., 1997; Suerte
et al., 2009; Sonntag et al., 2011). Open symbols are from the different lithologic units while shaded symbols are samples with geochronological data of the
corresponding lithological symbol with exception of the LMN sample (cross) which belongs to the LIC. Data from the Amacan Volcanic Complex and the Lamingag
Intrusive Complex are obtained from Yumul et al. (2017).
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
11

Suerte et al. (2009) documented that calc-alkaline diorites are geneti-
cally related to porphyry copper mineralization at Kingking. In the Co-
O district, located to the north of the study area, Sonntag et al. (2011)
reported calc-alkaline rocks hosting intermediate sulfidation epithermal
veins. Despite their regional geochemical similarities, all above-men-
tioned mineral deposits have different ages. Gold mineralization at
Masara is associated with Late Miocene magmatism, while porphyry
copper mineralization at Kingking is of Late Oligocene to Early Miocene
age (Suerte et al., 2009). In the Co-O district, the gold mineralization is
hosted by Oligocene magmatic rocks (Sonntag et al., 2011). Ad-
ditionally, the Boyongan-Bayugo porphyry copper deposit at Surigao, in
the northeastern part of Eastern Mindanao, is associated with late
Pliocene diorite porphyries (Braxton et al., 2012). This implies that the
gold-copper mineralization in the region is genetically associated with
different magmatic pulses from Oligocene to Pliocene times. However,
the host rocks generally have low- to medium-K calc-alkaline compo-
sitions, except for the Cateel Quartz Diorite which shows a wide range
of low- to high-K compositions.
Epithermal gold mineralization is structurally controlled by the NW
corridor of the Masara Fault Zone. The Early Miocene MFZ was prob-
ably reactivated by movements along the Philippine Fault Zone (PFZ)
during the Pliocene. This salient structure serves as the main conduit for
the mineralizing hydrothermal fluids in the district. The hydrothermal
fluids represent different pulses depositing massive sulfide, quartz-sul-
fide and quartz-carbonate veins along a dominantly NW-trend and, in
places, EW structures.
At Masara, the epithermal gold mineralization is hosted by all li-
thological units described above, except the Amacan Volcanic Complex.
The Plio-Pleistocene dacitic volcanism of the Amacan Volcanic Complex
post-dates the gold mineralization. Based on the age dating of miner-
alized host rocks of the gold mineralization vis-à-vis of the barren
Amacan Volcanic Complex, the epithermal gold mineralization post-
dates its Late Miocene host rocks but it pre-dates the formation of the
Plio-Pleistocene Amacan Volcanic Complex. The latest mineralizing
event is probably genetically related to the intrusion of the Lamingag
Intrusive Complex.
6. Conclusions
The new geological, geochronological and geochemical results
better constrain the tectonic history and metallogenic evolution of
Eastern Mindanao.
The tectonic history of the Masara Gold District involves a geo-
chemical transition from Eocene tholeiitic magmatism attributed to the
proto-Molucca Sea Plate to calc-alkaline magmatism in the Early
Miocene due to the subduction of the proto-Philippine Sea Plate. The
calc-alkaline magmatic pulses during the Middle to Late Miocene are
attributed to the subduction of the Molucca Sea Plate along the proto-
Halmahera Trench. Adakitic magmatism of the Plio-Pleistocene is
linked to the eruption of the Leonard Kniassef volcano.
In the Masara Gold District, gold mineralization is structurally
controlled by the NW-trending Masara Fault Zone, interpreted to have
already formed before the Early Miocene. The fault zone was re-
activated by movements along the Pliocene Philippine Fault Zone,
which subsequently served as the conduit for the precipitation of the
epithermal gold veins.
The gold mineralization in the region is directly associated with
low- to medium-K calc-alkaline magmatism. Mineralization in the
Masara Gold District is associated with Late Miocene intrusions and is
post-dated by the unmineralized Plio-Pleistocene Amacan Volcanic
Complex.
The recognition of Late Miocene intrusions with similar
Fig. 7. Rock/MORB normalized spidergram patterns of the different rock units with negative Zr, Ta, Nb and Ti anomalies and generally showing an enrichment in
LILE except for the tholeiitic Masara Formation (MF). Previously published geochemical data are also shown (e.g. Sajona et al., 1997; Suerte et al., 2009; Sonntag
et al., 2011; Yumul et al., 2017 for the AVC and LIC data plots). MF – Masara Formation, CQD – Cateel Quartz Diorite, AA – Alipao Andesite, LIC – Lamingag Intrusive
Complex, AVC – Amacan Volcanic Complex.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
12

Fig. 8. Harker diagrams illustrating that the samples of the Masara Gold District show a negative correlation between Al
2
O
3
, FeO, MgO, CaO, TiO
2
, P
2
O
5
and SiO
2
with increasing fractionation. AVC and LIC data are obtained from Yumul et al. (2017). Open symbols are from the different lithologic units while shaded symbols are
samples with geochronological data of the corresponding lithological symbol with exception of the LMN sample (cross) which belongs to the LIC.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
13

geochemical characteristics should guide future mineral exploration in
the Eastern Mindanao gold-copper province and possibly in areas with
similar geologic settings in the SW-Pacific.
Declaration of interests
The authors declared that there is no conflict of interest.
Acknowledgements
This study forms part of the United States Agency for International
Development through the Science, Technology, Research, and
Innovation for Development (USAID STRIDE) research grant (Grant No.
0213997-G-2015-019-00). Support provided by Apex Mining Co., Inc.
(AMCI) and the University of the Philippines - National Institute of
Geological Sciences (UP-NIGS) are gratefully acknowledged. Fieldwork
has been logistically supported by AMCI. Additional support was also
provided by the Society of Economic Geologists Graduate Student
Fellowship Grant (2015) to the senior author. Special thanks are also
given to Professor Khin Zaw for his suggestions and editorial handling,
Dr. Daniel Müller and an anonymous reviewer for the comprehensive
and constructive review which significantly improved this paper.
Appendix A. Whole rock K-Ar data of representative samples from the Lamingag Intrusive Complex and the Alipao Andesite. K-Ar dating
was done by Geochronex Analytical Services & Consulting.
Sample Formation Latitude Longitude *K% 40 Ar rad, nl/g %40 Ar air Age (Ma) Error 1σ
LMN JM 0505 05 LIC 7.364583° 126.048417° 1.16 0.314 95.1 7.1 0.2
CAL BVNP 060415 9D Alipao Andesite 7.381167° 126.129583° 0.70 0.38 97.9 14.2 1.4
UCX JSBC 641506 LIC 7.377028° 126.031694° 0.59 0.185 93.7 8.2 0.5
References
Aurelio, M.A., Barrier, E., Rangin, C., Muller, C., 1991. The Philippine fault in the late
Cenozoic evolution of the Bondoc-Masbate-N. Leyte area, central Philippines. J.
Southe. Asian Earth 6, 221–238.
Aurelio, M.A., 2000. Shear partitioning in the Philippines: constraints from Philippine
Fault and global positioning system data. Isl. Arc 9, 584–597.
Aurelio, M.A., Peña, R.E., Taguibao, K.J.L., 2013. Sculpting the Philippine archipelago
since the Cretaceous through rifting, oceanic spreading, subduction, obduction, col-
lision and strike-slip faulting: contribution to IGMA5000. J. Southe. Asian Earth 72,
102–107.
Barnett R., 1983. An evaluation of the Davao geothermal prospect. Philippine National
Oil Company and Energy Development Corporation internal report, 8 July 1983,
KRTA, Auckland, p. 62.
Basori, M.B.I., Zaw, K., Meffre, S., Large, R.R., 2016. Geochemistry, geochronology, and
tectonic setting of early Permian (∼290 Ma) volcanic-hosted massive sulphide de-
posits of the Tasik Chini district, Peninsular Malaysia. Int. Geol. Rev. 58, 929–948.
Braxton, D.P., Mathur, R., 2011. Exploration applications of copper isotopes in the su-
pergene environment: a case study of the Bayugo porphyry copper-gold deposit,
Southern Philippines. Econ. Geol. 106, 1447–1463.
Braxton, D.P., Cooke, D.R., Dunlap, J., Norman, M., Reiners, P., Stein, H., Waters, P.,
2012. From crucible to graben in 2.3 Ma: a high-resolution geochronological study of
porphyry life cycles, Boyongan-Bayugo copper-gold deposits, Philippines. Geology
40, 471–475.
Briqueu, L., Bougault, H., Joron, J.L., 1984. Quantification of Nb, Ta, Ti and V anomalies
in magmas associated with subduction zones: petrogenetic implications. Earth Planet.
Sci. Lett. 68, 297–308.
Castillo, P.R., 2012. Adakite petrogenesis. Lithos 134–135, 304–316.
Claveria, R.J.R., 2001. Mineral paragenesis of the Lepanto copper and gold and the
Victoria gold deposits, Mankayan Mineral District, Philippines. Res. Geol. 51,
97–106.
Chiaradia, M., 2015. Crustal thickness control on Sr/Y signatures of recent arc magmas:
an earth scale perspective. Sci. Rep. 8 (8115), 1–5.
Cooke, D.R., Simmons, S.F., 2000. Characteristics and genesis of epithermal gold deposits.
Rev. Econ. Geol. 13, 245–278.
Fig. 9. Schematic representation of the main tec-
tonic events forming the rocks of the Masara Gold
District in Eastern Mindanao. pMSP – proto Molucca
Sea Plate (dark green), pPT – proto Philippine
Trench, pT- Philippine Trench, WPB – West
Philippine Basin, pHT – proto Halmahera Trench,
PSP – Philippine Sea Plate (dark blue), MFZ –
Masara Fault Zone and MSP – Molucca Sea Plate
(orange). Legend: green – Masara Formation; red –
Cateel Quartz Diorite; light blue – Agtuuganon
Limestone; pink – Alipao Andesite; purple –
Lamingag Intrusive Complex; yellow – Amacan
Volcanic Complex. (For interpretation of the refer-
ences to color in this figure legend, the reader is
referred to the web version of this article.)
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
14

Defant, M.J., Drummond, M.S., 1990. Derivation of some modern arc magmas by melting
of young subducted lithosphere. Nature 347, 662–665.
Dickin, A.P., 1995. Radiogenic Isotope Geology. Cambridge University Press, Cambridge,
UK, pp. 490.
Gardiner, N.J., Robb, L.J., Morley, C.K., Searle, M.P., Cawood, P.A., Whitehouse, M.J.,
Kirkland, C.L., Roberts, N.M.W., Myint, T.A., 2016. The tectonic and metallogenic
framework of Myanmar: a Tethyan mineral system. Ore Geol. Rev. 79, 26–45.
Garwin, S., Hall, R., Watanabe, Y., 2005. Tectonic setting, geology, and gold and copper
mineralization in Cenozoic magmatic arcs of Southeast Asia and the West Pacific.
Soc. Econ. Geol. 100th Anniv. Volume, 891–930.
Hall, R., 1996. Reconstructing Cenozoic SE Asia. In: Hall, R., Blundell, D.J. (Eds.),
Tectonic Evolution of SE Asia. Geol. Soc. Spec. Publ., pp. 153–184.
Hall, R., 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW
Pacific: computer-based reconstructions, model and animations. J. Asian Earth Sci.
20, 353–434.
Hall, R., 2012. Late Jurassic-Cenozoic reconstructions of the Indonesian region and the
Indian Ocean. Tectonophysics 570–571, 1–41.
Hollings, P., Cooke, D.R., Waters, P.J., Cousens, B., 2011. Igneous geochemistry of mi-
neralized rocks of the Baguio District, Philippines: implications for tectonic evolution
and the genesis of porphyry-style mineralization. Econ. Geol. 106, 1317–1333.
Hunter, A.G., Blake, S., 1995. Petrogenetic evolution of a transitional tholeiitic calc-al-
kaline series: Towada Volcano, Japan. J. Petrol. 36, 1579–1605.
Imai, A., Suerte, L.O., Nishihara, S., 2009. Origin of bornite pods in intrusive rocks at the
Kingking porphyry copper-gold deposit, Southeastern Mindanao, Philippines. Res.
Geol. 59, 307–313.
Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification of the common
volcanic rocks. Can. J. Earth Sci. 8, 523–548.
Jego, S., Maury, R.C., Polve, M., Yumul Jr., G.P., Bellon, H., Tamayo Jr., R.A., Cotton, J.,
2005. Geochemistry of adakites from the Philippines: constraints on their origins.
Res. Geol. 55, 161–185.
Jimenez Jr., F.A., Yumul Jr., G.P., Maglambayan, V.B., Tamayo Jr., R.A., 2002. Shallow to
near-surface, vein-type epithermal gold mineralization at Lalab in the Sibutad gold
deposit, Zamboanga del Norte, Mindanao, Philippines. J. Asian Earth Sci. 21,
119–133.
Lee, T.Y., Lawver, L.A., 1995. Cenozoic plate reconstruction of Southeast Asia.
Tectonophysics 251, 85–138.
Ludwig, K.R., 2008. Isoplot 3.70. A Geochronological Toolkit for Microsoft Excel.
Berkeley Geochronology Center.
Ma, Q., Xu, Y.G., Zheng, J.P., Sun, M., Griffin, W.L., Wei, Y., Ma, L., Yu, X., 2016. High-Mg
adakitic rocks and their complementary cumulates formed by crystal fractionation of
hydrous mafic magmas in a continental crustal magma chamber. Lithos 260,
211–224.
MacDonald, G.D., Arnold, L.C., 1994. Geological and geochemical zoning of the Grasberg
igneous complex, Irian Jaya, Indonesia. J. Geochem. Explor. 50, 143–178.
MacDonald, R., Hawkesworth, C.J., Heath, E., 2000. The Lesser Antilles volcanic chain: a
study in arc magmatism. Earth Sci. Rev. 49, 1–76.
Macpherson, C.G., Dreher, S.T., Thirlwall, M.F., 2006. Adakites without slab melting:
high pressure differentiation of island arc magma, Mindanao, the Philippines. Earth
Planet. Sci. Lett. 243, 581–593.
Malicdem, D.G., Peña, R.E., 1966. Preliminary report on the geology and mineral deposits
of the Masara Mine Area, Mabini, Davao. Philippine Bureau of Mines, Manila.
Unpublished report, p. 18.
Malihan, T.D., Flores, R.A.L., 2012. Re-estimation of the 2011 Resource of Maco Mines
located in Maco, Compostela Valley Province, Southeastern Mindanao Island,
Philippines. Technical Report to the Philippine Stock Exchange, Manila, p. 98.
Malihan, T.D., Flores, R.A.L., Ruelo, H.B., 2015. Philippine vein-type deposits: key con-
cepts, parameters, and some examples in mineral resource/ore reserve estimation. J.
Geol. Soc. Phil. 70, 3–37.
Martin, H., Smithies, R.H., Rapp, R., Moyen, J.F., Champion, D., 2005. An overview of
adakite, tonalite-trondhjemite-granodiorite (TTG), and sanukitoid: relationships and
some implication for crustal evolution. Lithos 79, 1–24.
Mercado, A., Estoque, J.C., Lodringueza, L.A., Ribillion, F.C., 1987. Geology and ore
deposits of Masara mine, Davao del Norte, Philippines. In: Proceedings Pacific Rim
Congress ‘87, Australasian Institute of Mining and Metallurgy, Victoria, pp. 329–332.
MGB (Mines and Geosciences Bureau), 2010. Geology of the Philippines (2nd Ed.),
Quezon City, Philippines. Mines and Geoscience Bureau, p. 532.
Mitchell, A.H.G., Hernandez, F., Dela Cruz, A.P., 1986. Cenozoic evolution of the
Philippine Archipelago. J. Southe. Asian Earth 1, 3–22.
Mitchell, A.H.G., Leach, T.M., 1991. Epithermal Gold Systems in the Philippines: Island
Arc Metallogenesis. Geothermal Systems and Geology. Academic Press, London, pp.
457.
Miyashiro, A., 1974. Volcanic rock series in island arcs and active continental margins.
Am. J. Sci. 274, 321–355.
MMAJ-JICA (Metal Mining Agency of Japan – Japan International Cooperation Agency),
1973. Report on the geological survey of eastern Mindanao, Phase III, p. 305.
Moyle, A.J., Doyle, B.J., Hoogvliet, H., Ware, A.R., 1990. Ladolam gold deposit, Lihir
Island. In: F.E. Hughes (Ed.). Geology of the Mineral Deposits of Australia and Papua
New Guinea, Australasian Institute of Mining and Metallurgy, Parkville, Australia,
pp. 1793–1805.
Müller, D., Leander, F., Herzig, P.M., Hunt, S., 2001. Potassic igneous rocks from the
vicinity of epithermal gold mineralization, Lihir Island, Papua New Guinea. Lithos 57,
163–186.
Payot, B.D., Maglambayan, V.B., Dimalanta, C.B., Yumul Jr., G.P., Tamayo Jr., R.A.,
Matsuda, T., Suzuki, S., Bellon, H., 2005. Geology and hydrothermal alteration of the
low sulfidation Pantingan gold system, Mount Mariveles, Bataan (Luzon),
Philippines. Res. Geol. 55, 155–162.
PHIVOLCS (Philippine Institute of Volcanology and Seismology), 2016. Active faults and
trenches in the Philippines. URL: http://www.phivolcs.dost.gov.ph/index/php?
option=com_content&view=article&id=78&Itemid=500024. Last accessed 17 Nov
2016.
Pearce, J.A., Harris, B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for
the tectonic interpretation of granitic rocks. J. Petrol. 25, 956–983.
Pubellier, M., Quebral, R., Rangin, C., Deffontaines, B., Muller, C., Butterlin, J., Manzano,
J., 1991. The Mindanao Collision Zone: a soft collision event within a continuous
Neogene strike-slip setting. J. Southe. Asian Earth 6, 239–248.
Pubellier, M., Bader, A.G., Rangin, C., Deffontaines, B., Quebral, R., 1999. Upper plate
deformation induced by subduction of a volcanic arc: the Snellius Plateau (Molucca
Sea, Indonesia and Mindanao, Philippines). Tectonophysics 304, 345–368.
Qian, X., Feng, Q., Wang, Y., Chonglakmani, C., Monjai, D., 2016. Geochronological and
geochemical constraints on the mafic rocks along the Luang Prabang zone: carboni-
ferous back-arc setting in northwest Laos. Lithos 245, 60–75.
Quebral, R.A., 1994. Tectonique du segment meridional de la faille Philippine, Mindano
Oriental, Philippines; passage d’une zone de collision a une zone de decrochement.
Unpublished Ph.D thesis, Universite Pierre et Marie Curie, Paris, France.
Quebral, R.A., 1996. The onset of movement on the Philippine Fault in eastern Mindanao:
a transition from a collision to a strike-slip environment. Tectonics 15, 713–726.
Querubin, C.L., Yumul Jr., G.P., 2005. Mass change calculations as applied to the search
for volcanogenic massive sulfide deposits: an example from Malusok, Siocon,
Zamboanga del Norte, Mindanao, Philippines. Res. Geol. 55, 61–72.
Rangin, C., Spakman, W., Pubellier, M., Bijwaard, H., 1999. Tomographic and geological
constraints on subduction along the eastern Sundaland continental margin (South-
East Asia). B. Soc. Geol. Fr. 170 (6), 775–788.
Ronacher, E., Richards, J.P., Villeneuve, M.E., Johnston, M.D., 2002. Short life-span of
the ore-forming system at the Porgera gold deposit, Papua New Guinea: Laser
40
Ar/
39
Ar dates for roscoelite, biotite, and hornblende. Miner. Deposita 37, 75–86.
Sajona, F.G., Bellon, H., Maury, R.C., Pubellier, M., Quebral, R.D., Cotton, J., Bayon, F.E.,
Pagado, E., Pamatian, P., 1997. Tertiary and Quaternary magmatism in Mindanao
and Leyte (Philippines): geochronology, geochemistry and tectonic setting. J. Southe.
Asian Earth 15, 121–153.
Sajona, F.G., Maury, R.C., 1998. Association of adakites with gold and copper miner-
alization in the Philippines. Earth Planet. Sci. 326, 27–34.
Sajona, F.G., Izawa, E., Motomura, Y., Imai, A., Sakakibara, H., Watanabe, K., 2002.
Victoria carbonate-base metal gold deposit and its significance in the Mankyan
Mineral District, Luzon, Philippines. Res. Geol. 52, 315–328.
Saunders, A.D., Tarney, J., Weaver, S.T., 1980. Transverse geochemical variations across
the Antartic Peninsula: implications for the genesis of calc-alkaline magmas. Earth
Planet. Sci. Lett. 46, 344–360.
Seton, M., Muller, R., Zahirovic, S., Gaina, C., Torsvik, T., Shephard, G., Talsma, A.,
Gurnis, M., Turner, M., Maus, S., Chandler, M., 2012. Global continental and ocean
basin reconstructions since 200 Ma. Earth Sci. Rev. 113, 212–270.
Sillitoe, R.H., 1997. Characteristics and controls of the largest porphyry copper-gold and
epithermal gold deposits in the circum-Pacific region. Aust. J. Earth Sci. 44, 373–388.
Sillitoe, R.H., Hedenquist, J.W., 2003. Linkages between volcanotectonic settings, ore-
fluid compositions and epithermal precious deposits. Econ. Geol. Sp. Pub. 10,
315–343.
Sonntag, I., Kerrich, R., Hagemann, S.G., 2011. The geochemistry of host arc volcanic
rocks to the Co-o epithermal gold deposit, Eastern Mindanao, Philippines. Lithos 127,
564–580.
Soejima, T., 1999. Application of rock powder pellet analysis using high-sensitivity XRF
analysis machine and chemical weathering. Unpublished M.Sc. Thesis. Kyushu
University, pp. 35.
Suerte, L.O., 2007. The magmatism and hydrothermal system of the Kingking porphyry
copper deposit: an insight into the mineralization of the copper-gold belt in
Southeastern Mindanao, Philippines. Unpublished PhD Thesis. Kyushu University,
pp. 113.
Suerte, L.O., Imai, A., Nishihara, S., 2009. Geochemical characteristics of intrusive rocks,
Southeastern Mindanao, Philippines: implication to metallogenesis of porphyry
copper-gold deposits. Res. Geol. 59, 244–262.
Sufni, Hakim A., Hall, R., 1991. Tertiary volcanic rocks from the Halmahera Arc, Eastern
Indonesia. J. Southe. Asian Earth 6, 271–288.
Tsutsumi, Y., Horie, K., Sano, T., Miyawaki, R., Momma, K., Matsubara, S., Shigeoka, M.,
Yokoyama, K., 2012. LA-ICP-MS and SHRIMP ages of zircons in chevkinite and
monazite tuffs from the Boso Peninsula, Central Japan. B. Natl. Mus. N. Sc. S. C 38,
15–32.
UNDP (United Nations Development Programme), 1987. Geology and gold mineralization
of Surigao del Norte, Technical Report No. 4, p. 58.
Wang, Q., Xu, J.-F., Jian, P., Bao, Z.-W., Zhao, Z.-H., Li, C.-F., Xiong, X.-L., Ma, J.-L., 2006.
Petrogenesis of adakitic porphyries in an extensional tectonic setting, Dexing, South
China: implications for the genesis of porphyry copper mineralization. J. Petrol. 47,
119–144.
Waters, P.J., Cooke, D.R., Gonzales, R.I., Phillips, D., 2011. Porphyry and epithermal
deposits and
40
Ar/
39
Ar geochronology of the Baguio District, Philippines. Econ. Geol.
106, 1335–1363.
Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma
series and their differentiation products using immobile elements. Chem. Geol. 20,
325–343.
Wolfe, R.C., Cooke, D.R., 2011. Geology of the Didipio region and genesis of the Dinkidi
alkalic porphyry Cu-Au deposit and related pegmatites, Northern Luzon, Philippines.
Econ. Geol. 106, 1279–1315.
Wood, D.A., 1980. The application of a Th-Hf-Ta diagram to problems of tectono-mag-
matic classification and to establishing the nature of crustal contamination of basaltic
lavas of the British Tertiary volcanic province. Earth Planet. Sci. Lett. 50, 11–30.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
15

Wu, J., Suppe, J., Lu, R., Kanda, R., 2016. Philippine Sea and East Asian plate tectonics
since 52 Ma constrained by new subducted slab reconstruction methods. J. Geophys.
Res. – Sol. Ea. 121, 4670–4741.
Yumul Jr., G.P., Brown, W.W., Dimalanta, C.B., Ausa, C.A., Faustino-Eslava, D.V., Payot,
B.D., Ramos, N.T., Lizada, A.N., Buena, A.E., Villaplaza, B.R., Manalo, P.C., Queaño,
K.L., Guotana, J.M.R., Pacle, N.A.D., 2017. Adakitic rocks in the Masara gold-silver
mine, Compostela Valley, Mindanao, Philippines: different places, varying mechan-
isms? J. Asian Earth Sci. 142, 45–55.
Yumul Jr., G.P., Dimalanta, C.B., Marquez, E.J., Maglambayan, V.B., 2008. Tectonic
setting of a composite terrane: a review of the Philippine island arc system. Geosci. J.
12, 7–17.
Zahirovic, S., Seton, M., Muller, R.D., 2014. The Cretaceous and Cenozoic tectonic evo-
lution of Southeast Asia. J. Geophys. Res. – Sol Ea. 5, 227–273.
Zaw, K., Meffre, S., Lai, C., Burrett, C., Santosh, M., Graham, I., Takayuki, M., Salam, A.,
Kamvong, T., Cromie, P., 2014. Tectonics and metallogeny of mainland Southeast
Asia – a review and contribution. Gondwana Res. 29, 5–30.
A.E. Buena, et al. Journal of Asian Earth Sciences: X 1 (2019) 100007
16