Jeffrey Hedenquist

University of Ottawa · Department of Earth and Environmental Sciences

The Mankayan mineral district of northern Luzon, Philippines, hosts several significant ore deposits and prospects of various types within an area of ~25 km2, including the Far Southeast porphyry Cu-Au deposit, the Lepanto high sulfidation epithermal Cu-Au deposit, the Victoria intermediate sulfidation epithermal Au-Ag vein deposit, the Teresa epit...

Hypogene advanced argillic alteration, typically quartz-alunite with halos of kaolinite ± dickite and roots of pyrophyllite ± diaspore, forms in the epithermal environment from condensates of magmatic vapor that contain SO2 and HCl, which exsolved from an underlying intrusive source. The most aggressive, nearly isochemical leaching of the host rock...

Mineral exploration since 2005 in a previously underexplored region of southwestern Mongolia resulted in the definition of the Zuun Mod porphyry Mo-Cu deposit, followed by discovery of the Altan Nar and Bayan Khundii epithermal gold deposits along with several prospects and advanced exploration projects. These discoveries form the core of the emerg...

Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and –750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7...

The DeLamar – Silver City district in southwest Idaho consists of several epithermal deposits, spaced at ~5 km. Mining in the district began in 1863 at War Eagle-Silver City, and high-grade veins were discovered at DeLamar and Florida Mountain in 1889. Up to 1914, underground mining produced at least 0.55 Moz Au and 21 Moz Ag from DeLamar and Flori...

Porphyry systems include shallow intrusions (to 2-3 km depth) that have halos of biotite ± K-feldspar alteration; a lower temperature overprint of white mica ± chlorite alteration is common, plus stockworks of quartz veins and porphyry Cu ± Au mineralization. The hypersaline liquid that forms the potassic alteration is coupled to a low-density vapo...

This presentation was given in the Australian geohug series, and is available at: https://www.youtube.com/watch?v=xjaJg66xu0M We all are guilty of being a bit dogmatic about things at times. However, when it comes to exploring, we have to realize that the next prospect is not going to be like the last one in terms of geological characteristics. Th...

Advanced argillic minerals, as defined, include alunite and anhydrite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite, zunyite, and topaz), and diaspore. One or more of these minerals form in five distinctly different geologic environments of hydrolytic alteration, with pH 4–5 to <1, most at depths <500 m. (1) Where an i...

Advanced argillic alteration, defined by Hemley as advanced hydrolytic, includes alunite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite), diaspore, anhydrite, and zunyite and topaz. One or more of these minerals form in five distinctly different acidic (pH ≤1 to 4-5) geologic environments, most at depths <500 m (Fig. 1)....

Alteration mineralogy from shortwave infrared (SWIR) spectroscopy was compared with X-ray diffraction (XRD) analyses for samples from the Zhengguang intermediate sulfidation epithermal Au-Zn deposit, eastern Central Asian orogenic belt, northeast China. The SWIR and XRD analyses indicate that alteration minerals in the vein-adjacent halo mainly com...

Advanced argillic alteration, defined by Hemley as advanced hydrolytic, includes alunite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite), diaspore, anhydrite, and zunyite and topaz. One or more of these minerals form in five distinctly different acidic (pH ≤1 to 4-5) geologic environments, most at depths <500 m (Fig. 1)....

Epithermal precious metal deposits form at shallow depths, <1 km. In volcanic arcs, these deposits are linked to deeper porphyritic intrusions and exsolved magmatic fluids. To understand how – and where – epithermal deposits form, we need to examine the link to the deeper system, which potentially includes porphyry copper deposits. The video of the...

The presentation reviews case histories of epithermal gold deposit discoveries, and why some of the first companies assessing a prospect failed when later companies made the discovery. The video to accompany these slides is available at: https://www.youtube.com/watch?v=uVZgvMqO8qw

Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/39Ar total gas age of 40.64 ± 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with qua...

Environments of advanced argillic alteration: I) mineral stabilities, and hypogene formation Jeffrey W. Hedenquist (Univ. Ottawa) and Antonio Arribas R. (Akita Univ.) Advanced argillic alteration, as defined, includes alunite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite) plus diaspore, andalusite, zunyite, and topaz. Groups of...

Advanced argillic alteration forms in five various (1-5), mainly shallow acidic environments, producing a variety of minerals that can include kaolinite, alunite and pyrophyllite. In addition to hypogene environments (1, 2), discussed elsewhere, boiling of a geothermal liquid generates ascending vapor with CO2 and H2 S. Where the vapor condenses in...

Fifty years of study of volcanoes and young porphyry systems provides the framework to interpret aqueous fluids associated with intrusion-centered deposits. 1970s studies of hydrothermal biotite from porphyry deposits concluded that magmatic water had a composition of -40 to -80 ‰ D/H, consistent with igneous biotite from the Boulder batholith quar...

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract For econ...

The Mankayan district, one of the richest mining districtsin the Philippines, is located in the Cental Cordillera of Northern Luzon. The district contains numerous porphyry Cu-Au deposits (Far Southest, Guinaoang, Buaki), a high-sul dation Cu-Au deposit (Lepanto) and intermediate-sul dation Victoria veins. This study concerns the Far Southeast porp...

Preparation of a textbook on the subject of economic geology is a daunting task due to the broad range of topics that must be covered in a consistent and balanced fashion, with an adequate understanding of each topic to provide a clear explanation to nonspecialists. Michel Jébrak and Éric Marcoux tackled this task and have done a commendable job. I...

Epithermal precious (± base) metal deposits are largely hosted by volcanic rocks, and the tops of ore bodies formed within 10s to several 100s m of the paleosurface (Lindgren, 1933) in hydrothermal systems driven by magmatic intrusions. There is a large variation in the style of epithermal deposits, including the associated alteration minerals, tha...

Epithermal precious (± base) metal deposits are largely hosted by volcanic rocks, and the tops of ore bodies formed within 10s to several 100s m of the paleosurface (Lindgren, 1933) in hydrothermal systems driven by magmatic intrusions. There is a large variation in the style of epithermal deposits, including the associated alteration minerals, tha...

Volcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju-Hatchobaru and Kirishima, Kyushu, host active magmatic-hydrothermal systems that are several km in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5-10 km depth over a period on the order of ~10e5 years. These hydrot...

The general features of ore deposits in the epithermal environment are influenced by their tectonic, magmatic and geologic associations. Geologic variability means that there is a wide variation in features associated with individual districts, deposits, and prospects. In this presentation we review some of the first-order features relevant to expl...

The Nansatsu-style deposits in southern Kyushu are type examples of volcanic arc-related enargite-gold deposits around the world. The ore minerals are hosted by residual quartz – resulting from nearly isochemical leaching by pH<2 fluid – with halos of advanced argillic alteration, including alunite (pH 2-4). Isotopic compositions of alunite in Nans...

The world-class Far Southeast (FSE) porphyry system, Philippines, includes the FSE Cu–Au porphyry deposit, the Lepanto Cu–Au high-sulfidation deposit and the Victoria–Teresa Au–Ag intermediate-sulfidation veins, centered on the intrusive complex of dioritic composition. The Lepanto and FSE deposits are genetically related and both share an evolutio...

Some scientists and journalists, and many members of the general public, have been led to believe that the world is rapidly running out of the metals on which our modern society is based. Advocates of the peak metal concept have predicted for many decades that increasing consumption will soon lead to exhaustion of mineral resources. Yet, despite ev...

Ore deposit models are important to provide concepts to guide us to area selection, but as they are simplistic and inflexible, they should not be taken into the field. Prospects – as well as the few (<<1%) that become ore deposits – are variations on a theme, and using a model to site drill holes, rather than interpreting what the rocks are and imp...

Porphyry systems include shallow intrusions (to 2-3 km depth) that have potassic alteration halos and porphyry Cu-Au mineralization associated with stockworks of quartz veins; a lower temperature phyllic overprint of white mica alteration is common. The hypersaline liquid that formed the potassic alteration is coupled to a low-density vapor phase t...

President Foster, SEG members, and friends: Introducing Richard Sillitoe to economic geologists is an easy task, since most are familiar with his published record on ore deposits. Many here today have heard Dick speak at previous conferences, and the fortunate ones have spent time in the field with him on assignments, assessing the potential of pro...

1) Introduction: Processes, and epithermal to porphyry transition 2) Epithermal and porphyry discoveries in Peru 3) The discovery potential in Miocene volcanic arcs of Peru

Most significant porphyry copper deposits known in Mexico are Laramide in age, largely Paleocene to early Eocene. These are located mainly in northern Mexico; there are a few younger porphyry deposits, of late Eocene and Pliocene age, in central and SE Mexico, respectively. By contrast, major epithermal deposits that are preserved formed in the lat...

Introduction Most significant porphyry copper deposits known in Mexico are Laramide in age, largely Paleocene to early Eocene. These are located mainly in northern Mexico; there are a few younger porphyry deposits, of late Eocene and Pliocene age, in central and SE Mexico, respectively. By contrast, major epithermal deposits that are preserved form...

Recent diamond drilling of 96 holes (~102 km) by Far Southeast Gold Resources Inc. at the Far Southeast Cu-Au porphyry deposit provides a 3-D exposure of the deposit and orebody (500 to –300 m elevation at 2 g/t gold equivalent), enabling new observations of the transition downward from high-sulfidation epithermal alteration and mineralization to t...

The Far-Southeast porphyry Cu-Au deposit, northern Luzon, Philippines, is hosted within the Imbanguila diorite – dacite intrusion complex and formed at 1.3-1.4 Ma, making this one of the youngest porphyry deposits in the world. Far Southeast Gold Resources Inc, a joint venture of Lepanto Consolidated Mining Company and Gold Fields Ltd, recently com...

Epithermal deposits (Au or Ag dominant, ± base metals) form within ~1 km of the surface in volcanic belts, both arcs and rifts, with the different tectonic settings refl ected in distinctly different characteristics. Within arcs, deposits are typically intrusion centred and commonly associated with hypogene advanced argillic alteration, both in lit...

Epithermal deposits (Au or Ag dominant, ± base metals) form within ~1 km of the surface in volcanic belts, both arcs and rifts, with the different tectonic settings reflected in distinctly different characteristics. Within arcs, deposits are typically intrusion centered and commonly associated with hypogene advanced argillic alteration, both in lit...

Madame President, SEG members and guests: I thank Larry Meinert for his citation for the SEG Ralph W. Marsden Award, both for what he said and what he left unsaid. It was Sam Adams who, as chair of the Committee on Committees, invited me to work on the SEG Membership Committee under the leadership of Bruce Bouley back in the early 1990s. This was...

Variable characteristics of ore deposits in the epithermal environment: Causes, and exploration implications Jeffrey W. Hedenquist 2501-160 George Street, Ottawa, ON K1N9M2, Canada 1 Introduction The general features of ore deposits in the epithermal environment are influenced by their tectonic, magmatic and geologic affiliations (Sillitoe and Hede...

Exploration for epithermal precious metal deposits (separate extended abstract)

Porphyry systems and ore deposits: A series of undergraduate lecture slides, presented in 2014 at the University of Ottawa and annotated in 2016

Epithermal systems and ore deposits: A series of annotated undergraduate lecture slides, presented at the University of Ottawa in 2014, and annotated in 2016

Sulfide scale is precipitating at 2770 m depth and ∼330 °C in well RN-17B from unboiled, seawater-dominated hydrothermal fluids. The scale consists of well-crystallized pyrrhotite with minor sphalerite, and traces of galena, pyrite, and chalcopyrite. Gold concentrations in the bulk sulfides reach 40 ppm, and Ag concentrations reach 20 ppm. In anoth...

Residual quartz and advanced argillic alteration form due to leaching by acidic condensates of volcanic vapors. Condensates of the vapors at Satsuma Iwojima were reacted theoretically with the host rhyolite in order to model the chemical composition during cooling from 350 to 100 C; the composition of the reacted fluid at 100 C and a pH of about 1...

The northern Pacific Rim—for the purposes of this contribution—comprises the Mesozoic and Cenozoic magmatic-arc and associated terranes of eastern China, Korea, Japan, the Russian Far East, Alaska, Yukon, British Columbia, the western United States, and Mexico. This ~1,800-km-long segment of the Pacific Rim is marked by a broad spectrum of metallog...

We report the first laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) study of trace element substitution in enargite. Results indicate significant variability in the composition of enargite samples from a single ore system. Samples come from the Mankayan district, Philippines, which hosts the Lepanto high-sulfidation Cu-Au de...

Seawater-dominated fluids discharge from the subaerial Reykjanes geothermal system, Iceland. There is a sharp pressure decrease in surface pipes at an orifice (throttle point), and Cu-rich scales deposit at this orifice that consist largely of bornite and digenite, along with sphalerite and other sulfides. The bornite and digenite form complex inte...

Gold deposits are arguably more widely distributed through geological time, and present in more geological environments, than the economic concentrations of any other metal. Hence, gold occurs in both a majority of countries worldwide and a spectrum of deposit types. Nevertheless, current production is dominated by mines in just four countries: Chi...

Seafloor hydrothermal systems precipitate Cu, Zn, and Fe sulfides at and below black smoker vents on the seafloor; as a result, the metal concentrations in the vent fluids are minimum values. We sampled deep, unboiled liquids from the Reykjanes geothermal reservoir, Iceland, and measured the metal concentrations. This active, seawater-dominated sys...

This book reviews hydrothermal mineral deposits and related processes, as implied by the title. However, it also includes an introduction to a potpourri of topics, from hydrothermal principles and fluids, hydrothermal alteration, and tectonic settings of mineral deposits, through description of several styles of mineral deposits, to the relationshi...

Publication review, by Jeffrey W. Hedenquist Resource Geology 58(2):203-203 · June 2008 Mineral Resources Map of East Asia (1:3,000,000) M. Kamitani, K. Okumura, Y. Teraoka, S. Miyano and Y. Watanabe Tsukuba: Geological Survey of Japan, AIST, 2007 ¥2415 This 1:3,000,000-scale map presents a compilation of the mineral resources of East Asia in tw...

The Oyu Tolgoi porphyry Cu-Au system in the South Gobi desert, Mongolia, comprises five deposits that extend over 6 km in a north-northeast–oriented zone. They occur in a middle to late Paleozoic arc terrane and are related to Late Devonian quartz monzodiorite intrusions. The Hugo Dummett deposits are the northernmost and deepest, with up to 1,000...

Roşia Montană, Romania, is Europe’s largest gold deposit, with a current identifıed resource of ~400 Mt at 1.3 g/t Au and 6 g/t Ag. The deposit is hosted by a Miocene age maar-diatreme complex emplaced into Cretaceous flysch-type sedimentary rocks and intruded by dacite domes. High-resolution 40Ar/39Ar dating of adularia associated with gold-bearin...

A series of large hydrothermal eruptions occurred across the Waiotapu geothermal field at about the same (prehistoric) time as the ~AD1315 Kaharoa rhyolite magmatic eruptions from Tarawera volcano vents, 10–20km distant. Triggering of the Waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent Ngapouri Fault. The K...

From the first issue in 1905 onward, Economic Geology has been the main publication for those who study mineral deposits; indeed, it is now difficult to imagine economic geology without Economic Geology. It is interesting to ask, therefore, Who were the farsighted people who founded the journal, and Why did they think a specialized publication devo...

The Gandy and Abolhassani epithermal precious and base metal deposits occur in the Torud-Chah Shirin mountain range in the Alborz magmatic belt of northern Iran. The mountain range is considered to be part of the Paleogene Alborz volcanic arc. The exposed rocks in the study area consist of a volcaniclastic sequence of thin-bedded siltstones and san...

Subduction of Tethyan oceanic crust produced voluminous arc rocks; the NW-trending Urumieh-Dokhtar belt in central Iran and the Alborz belt in northern Iran. The belts host many precious and base metal prospects. This paper documents the Gandy and Abolhassani prospects in the Alborz belt. The hosting Eocene volcanic rocks show a typical arc geochem...

The principal purpose of this report is to highlight the mineral potential in eight target countries of East and Central Asia: China, Mongolia, Vietnam, Laos, Kazakhstan, Kyrgyzstan, Uzbekistan, and Tajikistan. The target countries constitute one-third of the area of Asia, or 11% of the world’s explorable land surface, and contain regions of all ge...

Use of the concept of “sulfidation state,” in parallel with oxidation state, in the study of ore deposits finds its beginnings with the studies of Reno Sales and Charles Meyer at Butte, Montana. Experimental determination of the stability of sulfide minerals in terms of ƒS2 and temperature followed, leading to definition of contrasts in ore-forming...

Epithermal Au and Ag deposits of both vein and bulk-tonnage styles may be broadly grouped into high-sulfidation (HS), intermediate-sulfidation (IS), and low-sulfidation (LS) types based on the sulfidation states of their hypogene sulfide assemblages. The HS and LS types may be subdivided using additional parameters, particularly related igneous roc...

Most skarn ore deposits are characterized by two distinctly different alteration styles. An early prograde stage with anhydrous minerals, such as garnet and pyroxene, forms from relatively high-temperature, hypersaline liquid. A later retrograde stage with hydrous minerals, such as epidote, amphibole, and chlorite plus sulfide ore minerals, forms f...

We examined in detail the mineralogic and stable isotope characteristics of alteration minerals exposed at the surface of the El Salvador porphyry copper deposit. A total of 276 samples was collected from 203 localities over an area of >5 km2 at elevations between 2,900 and 3,300 m. The alteration assemblages can be separated into two groups, broad...

This report was produced in 2001 for the Metal Mining Agency of Japan, a governmental body that supports research on and exploration for mineral resources. The Middle Eastern region of western Asia contains major ore deposits, but it is far from adequately explored. Exploration has been patchy across much of the region, and in most countries inadeq...