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Goldschmidt 2021 Abstract
https://doi.org/10.7185/gold2021.4107
Hydrothermal fluorapatite in
magnesian skarns from Valea Rea
(Budureasa, Bihor Mountains,
Romania)
STEFAN MARINCEA, ADRIAN IULIAN IULIAN PANTIA,
DELIA-GEORGETA DUMITRAS, CRISTINA SAVA GHINET
AND ANDRA ELENA FILIUTA
Geological Institute of Romania
Presenting Author:
smarincea@yahoo.com
The occurrence of magnesian skarn from Valea Rea occurs in
the close proximity of the southern contact of the Budureasa
laccolith (-74 ± 3 to -73 ± 3 Ma according to K-Ar ages) with
Anisian dolostones pertaining to the Ferice Unit. Well-shaped
crystals of fluorapatite were identified in forsterite- and
phlogopite-bearing skarns located on the waste dump of an
exploration shaft, dug in the late 1980’s near the southern contact
of the intrusive body. The coordinates of the shaft entry, known
as “Shaft 2”, are N 46°39’49” – E 22°36’44”. Fluorapatite and
rare fluorite (Ca
0.9984Mn0.001Ni0.001F2) were identified as swarms
of crystals or agglomerations in calcite veins that crosscut the
skarn. Individual crystals have columnar habit, are of up to 1mm
in length and 0.3 mm in width, having a simple combination of
forms consisting of prisms {100} and low pyramids {101}. The
average composition resulting from the EMPA analyses on ten
different samples is (in wt.%): P
2O5 = 42.05, SiO2 = 0.09, Ce2O3
= 0.03, La
2O3 = 0.03, CaO = 55.40, MnO = 0.02, FeO = 0.04,
MgO = 0.03, F = 4.52, Cl = 0.01, O
≡
(F, Cl) = -1.91, Total =
100.31. Normalized to 3 (P+Si) and 13 (O+F+Cl)
pfu, this yields
to the formula:
(Ca4.989Mn0.001Fe2+0.003Mg0.003Ce0.001La0.001)(P2.992Si0.008)
(O
11.894F1.202Cl0.001).
The cell parameters of two representative samples are: a =
9.385(7) Å and
c = 6.891(9) Å, and a = 9.382(4) Å and c
=
6.889(5) Å, respectively. The indices of refraction, taken as mean
of measurements on ten different grains, are: w = 1.634(2) and e
= 1.631(1).
The calculated densities of the same two
representative samples are
Dx’ = 3.196 g/cm3 and Dx’’
= 3.202
g/cm
3, respectively, resulting in a mean density Dx
= 3.199
g/cm
3, which compares well with the measured density, Dm =
3.201(3) g/cm
3. Calculation of the Gladstone-Dale compatibility
indices gave in all cases values indicative of superior agreement
between physical and chemical data. In the infrared spectra, the
multiplicity of the bands assumed to phosphate modes (2
ν1 +
3
ν2+5ν3+5ν4) agrees with the reduction of the symmetry of PO43-
ion from
Td to Cs.