First report on the occurrence of CO2-bearing fluid inclusions in the Meiduk porphyry copper deposit, Iran: implications for mineralisation processes in a continental collision setting
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Date
2013-12-30
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Bogucki Wydawnictwo Naukowe
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Abstract
Hydrothermal alteration of the Meiduk porphyry copper deposit, south of the Kerman Cenozoic magmatic arc and
southeast of the central Iranian volcano-plutonic belt has resulted in three stages of mineralisation characterised by
veins and veinlets. These are, from early to late: (1) quartz + K-feldspar + biotite + pyrite ± chalcopyrite ± pyrrhotite
± magnetite (early potassic alteration and type-A veins); (2) quartz + chalcopyrite + pyrite + bornite + pyrrhotite + K-
-feldspar + biotite + magnetite (potassic-sericitic alteration and type-B veins); and (3) quartz + pyrite + chalcopyrite +
sericite (sericitic alteration and type-C veins). Most ores were formed during stages 2 and 3.
Three main types of fluid inclusions are distinguished based on petrographical, microthermometrical and laser Raman
spectroscopy analyses, i.e. type I (three-phase aqueous inclusions), type II (three-phase liquid-carbonic inclusions) and
type III (multi-phase solid inclusions). The fluid inclusions in quartz veins of the stages are mainly homogenised at
340–530°C (stage 1), 270–385°C (stage 2) and 214–350°C (stage 3), respectively, with salinities of 3.1–16 wt.% NaCl equivalent,
2.2–43 wt.% NaCl equivalent and 8.2–22.8 wt.% NaCl equivalent, respectively.
The estimated trapping pressures are 97.9–123.6 MPa (3.7–4.6 km) in stage 1 and 62.5–86.1 MPa (2.3–3.1 km) in stage 2,
respectively. These fluid inclusions are homogenised in different ways at similar temperatures, suggesting that fluid
boiling took place in stages 2 and 3. The fluid system evolved from high-temperature, medium-salinity, high-pressure
and CO2-rich to low-temperature, low-pressure, high-salinity and CO2-poor, with fluid boiling being the dominating
mechanism, followed by input of meteoric water. CO2 escape may have been a factor in increasing activities of NaCl and
S2- in the fluids, diminishing the oxidation of the fluids from stage 1 to 3. The result was precipitation of sulphides and
trapping of multi-phase solid inclusions in hydrothermal quartz veins.
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Keywords
CO2-bearing fluid inclusions, laser Raman spectroscopy, collision, Meiduk porphyry copper deposit, Iran
Citation
Geologos, 2013, vol. 19, 4, pp. 301-320
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ISBN
978-83-232187-4-6
ISSN
1426-8981