Basem Ahmed Zoheir_Barramiya, OGR_2011.pdf

ange of temperatures, commonly between 337 and 362 °C with a
pronounced cluster around 350 °C. Bulk compositions, density, and
isochores were calculated from microthermometric and Raman data
using the Flincor program (Brown, 1989) and the equation of Bowers
and Helgeson (1983) for the aqueous-carbonic inclusions. The
carbonic phase is composed of a mixture of variable proportions of
CH4 and CO2, an interpretation confirmed by micro-Raman spectroscopy
(Fig. 9b, c). The bulk composition of the aqueous-carbonic
inclusions based on the microthermometric measurements and
Raman data is X CO2: 4–43 mol% (typically 25–40 mol%); X H2O: 55–
96 mol% (typically 65–80 mol%); XCH4: b15 mol%; XN2: b4 mol%;and
X NaCl: 1–2 mol%. CO 2 densities vary from 0.78 to 0.88 g/cm 3 ;bulk
densities are mainly in the range of 0.86–0.99 g/cm 3 ; and salinity
varies from 1.5 to 8.2 wt.% NaCl equiv.
7.2. P–T conditions
The presence of CH 4 and/or N 2 in the CO 2–H 2O–salt system may
affect some microthermometric properties and can cause misestimate
B. Zoheir, B. Lehmann / Ore Geology Reviews 39 (2011) 101–115
Table 1
Representative EPMA data of sulfide minerals disseminated in the Barramiya quartz lodes and adjacent wallrocks.
Arsenopyrite
Fe 35.07 34.46 34.55 34.47 34.45 35.17 34.32 34.75 34.33 35.33 35.26 35.62 35.49 35.48 35.07
S 22.72 21.88 21.05 22.19 21.27 23.03 21.61 22.03 22.13 22.03 23.15 23.01 21.46 23.02 22.93
As 42.21 42.08 43.30 42.09 43.24 40.92 42.07 41.90 41.96 42.54 41.67 41.77 42.35 41.68 41.40
Ni – 0.23 0.20 0.24 0.41 0.13 0.27 0.38 0.13 – – – – – 0.10
Cu – – – 0.04 0.05 – – – 0.02 – – – – – –
Ag – – 0.03 – 0.22 0.21 – 0.21 – – – – – – 0.19
Te – – – – – 0.04 – – – – – – – – –
Au 0.21 0.13 0.17 0.16 0.02 0.05 0.08 0.16 0.12 – – – – – –
Sb – 0.07 0.02 – 0.06 0.19 – 0.07 – – – – – – 0.09
Sum 100.01 98.78 99.32 99.25 99.73 99.71 98.37 99.41 98.73 99.91 100.1 100.4 99.30 100.2 99.80
Pyrite
Fe 46.04 46.13 46.04 46.47 46.44 46.60 47.80 46.50 46.65 47.49 46.87 46.00 46.04 46.44 46.91
S 52.26 53.86 53.89 53.93 53.82 52.43 52.81 52.04 52.28 51.33 52.24 51.29 51.27 52.77 52.26
As 1.57 0.22 – – – 0.37 0.05 0.22 0.05 0.22 0.22 0.18 0.22 0.67 –
Co – – – – – – – – – – – – – – –
Ni – 0.69 0.14 0.04 0.09 0.05 0.11 – – 0.06 0.23 – 0.20 0.33 0.14
Cu – – – – – – – – – – 0.61 – – – –
Ag 0.04 0.04 0.05 0.04 0.04 – 0.04 – – – – – – – 0.03
Te – – 0.02 – – – – – – 0.03 – – – – –
Au 0.09 0.02 – – – 0.03 0.06 – 0.02 – – – – – –
Sum 99.95 100.3 100.0 100.5 100.4 99.51 100.8 98.79 99.04 99.15 99.40 97.48 97.58 99.95 99.25
Chalcopyrite Sphalerite
Fe 29.97 30.39 30.68 29.85 30.80 30.60 30.77 29.93 3.56 3.23 3.36 2.51 3.18 3.08 3.04
S 34.73 34.88 34.30 34.42 34.61 34.25 34.79 35.27 32.31 32.71 32.44 32.67 32.53 32.59 32.56
As – 0.10 0.48 0.33 0.40 0.45 0.34 – – – – – – – –
Ni – – 0.08 – 0.32 0.30 0.29 0.02 – – – – – – –
Cu 33.85 33.21 33.39 33.75 33.06 33.90 33.07 33.81 1.04 1.96 0.98 1.04 1.29 1.35 1.20
Zn 0.05 0.03 0.04 0.06 0.03 0.05 0.03 0.03 62.43 60.74 62.51 62.48 62.04 61.94 62.24
Ag 0.04 0.04 0.02 0.04 0.04 0.04 0.03 0.05 – 0.02 – – – – –
Te – – – 0.02 – – – 0.02 – – – – – – –
Au 0.09 0.12 – – – – – – – – – – – – –
Sum 98.65 98.66 98.99 98.47 99.27 99.59 99.39 99.12 99.36 98.65 99.44 98.76 99.05 98.98 99.06
Sb-bearing Fe-gersdorffite (Ni,Fe)AsS Tetrahedrite–freibergite Gold
Fe 9.26 6.61 8.71 7.87 9.69 10.70 3.78 3.29 3.59 3.80 4.12
S 19.96 19.55 19.80 19.74 19.95 19.88 17.39 17.27 17.21 16.98 16.17
As 46.14 45.96 45.86 45.76 46.82 46.17 0.54 0.57 0.56 0.26 0.58
Co 0.69 0.50 0.62 0.60 0.66 0.64 – – – – –
Ni 22.37 26.68 24.48 25.52 21.30 22.32 – – – – –
Cu – – – – – – 21.97 21.39 21.72 21.36 21.90
Zn – – – – – – >1.32 >2.16 1.62 1.10 0.96
Ag – – – – – – 31.45 30.59 30.91 31.54 29.45 12.60 12.47 11.69 7.27
Te – – – – – – – – – – – – – – –
Au – – – – – – 0.23 0.11 – – – 86.72 87.51 87.89 92.31
Sb 0.16 0.24 0.19 0.20 0.15 0.17 24.96 24.73 24.77 25.44 25.33 – – – –
Sum 98.60 99.56 99.68 99.71 98.60 99.89 101.4 100.0 100.4 100.5 98.51 99.32 99.98 99.58 99.58
– below detection limit.
of fluid salinity, density, and trapping pressures (Van den Kerkhof and
Thiéry, 2001). However, the consistency of the salinity data precludes
significant influence of the CH4 and N2 contents, except for a few
T mclath values N10 °C that are likely related to the presence of
appreciable amounts of CH4. As such, the salinities determined from
the largely predominant group of inclusions are considered as good
estimate of the composition of the ore fluid. Using the isochores for
the aqueous-carbonic inclusions, the formation temperatures of the
auriferous quartz lodes range from 325 to 370 °C under pressures of
1.3–2.4 kbar (Fig. 9d).
7.3. Entrapment mechanism
Criteria including comparable T hCO2 and T mCO2 ranges of the
aqueous-carbonic and carbonic inclusions, presence of similar
amounts of CH 4 ±N 2 in both types, and their identical Raman data
suggest that these inclusions trapped the same fluid as synchronous
inclusions (sensu Fonarev et al., 1998). Variations in phase ratios,
temperature of homogenization of the carbonic phase and in total
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