Geological and Geophysical Studies of Sulfide Copper Mineralization in the Dochileh Area: An Example of Manto‐Type Deposit in the Sabzevar Zone, Iran
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Abstract The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rock displays two hydrothermal events: zeolite–carbonate alteration that is a stratigraphic–lithologic feature and chlorite and chlorite/ferruginous alterations in the local mineralized structures. Ore formation is related to both hydrothermal events and occurs in both stratiform and vein mineralization types. Mineralization consists of main chalcocite with variable amounts of bornite, chalcopyrite, native copper, malachite, and cuprite minerals, which occur as hydrothermal breccias, and disseminated, vein, and veinlet forms. Geophysical field studies using resistivity and induction polarization (IP) methods were conducted along nine survey lines in the area. As a result of modeling and interpretation of the acquired geophysical data, high values of IP and resistivity corresponding to mineralization were observed at two depth levels: 0–20 m and more than 40 m. Based on these geological and geophysical investigations, six locations for drilling exploration boreholes were proposed. Drilling data confirmed the mineralization containing high copper values in the two depth levels: the vein‐type mineralization in the surface and shallow depth level, and the stratiform mineralization at the deeper level. Fluid inclusion studies in calcite and quartz from stratiform‐ and vein‐type mineralization show the evidence of mixing, and a linear dilution trend during the ore formation occurred at a wide range of temperatures: 121–308°C and 80–284°C, respectively, and varying salinities of between 3.2–16.8 and 0.8–22 wt% NaCl equivalents. The stable isotope composition of δ 34 S that falls in a range of −2.4 to +25.0‰ could be considered biogenetic sulfur from bacterial sulfate reduction and leaching of sulfur from hosting basalt. The δ 13 C values of calcite vary between −0.6 and −7.6‰, suggesting a major contribution of marine carbonates associated with igneous carbonates, and the δ 18 O SMOW values of calcite are between +15.2 and +19.9‰, suggesting a contribution of δ 18 O‐rich sedimentary rocks and δ 18 O‐poor meteoric water. Copper and sulfide‐rich hydrothermal fluid have flowed upward through the local faults and permeable interbeds within the Eocene volcanic sequence and have formed the mineralized veins and horizons. The geophysical results have detected the local faults as the channel ways for mineralization.Keywords:
Bornite
Hypogene
Chalcocite
Lithology
Prospecting
Malachite
Breccia
The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1961)
The authors have arrived at the following results upon studying the idaite-bearing ores from ten different localities in Japan. 1) Idaite have been found in several deposits in Japan. The specimens from Yakuwa Mine, Yamagata Prefecture, have been unequivocally identified by X-ray powder method. The number of sites yielding idaite in Japan is expected to increase with further study. 2) Idaite occurs in the secondary enrichment zone of copper deposit in the form of secondary decomposition product of chalcopyrite and bornite, except in two sites, where it is present as final crystallization product in copper deposits formed under low temperature and pressure. 3) Hypogene idaite is contained in small quantity in bornite, together with digenite and chalcopyrite. Supergene idaite forms lattices, lamellae and veinlets buried in chalcopyrite and bornite. In some cases, it forms films between chalcopyrite and supergene chalcocite, or replaces pyrite in company with supergene chalcocite, digenite and covellite. 4) The process of secondary enrichment and oxidation of chalcopyrite and bornite may be summarized as follows; chalcopyrite→supergene bornite hypogene bornite idaite chalcocite digenite→covellite cuprite tenorite native copper
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This study was planned with the aim of identifying the nature and circumstances of the high-graded central core and increasing trend of copper content through depth of 1000 m in Miduk PCD. Mechanisms of high-grading, refer to hypogene enrichment (HE), in PCDs poorly understood. Two main hypotheses for hypogene enrichment formation assumed addition of extra copper to the system, alternatively hypogene leaching and enrichment. In order to obtain alteration-mineralization-geochemical pattern both horizontally and vertically, all macroscopic data extracted from relogging of 6800 m' drill core along an east-west profile, compiled with microscopic observations from studying of 550 thin-polished sections and copper grades of 3400 samples analyzed by XRF and ICP-OES. Our findings proved hypogene enrichment events at deposit. HE evidences in macroscopic and microscopic scales identified almost as various replacement textures between Fe-Cu sulphides and also vein-reopening by later Cu-mineralization and new generation of disseminated or vein type mineralization. In addition, appearance of dark halo, as consuming intermediate chalcocite phase, around pyrite and chalcopyrite which gradually evolves as bornite, also extruding extra iron as fibrous hematite at the outer edge of bornite product replaced chalcopyrite, partially replacement of bornite and chalcopyrite to hypogene chalcocite and covellite-digenite in deep potassic are other HE evidences in the case study. Here, we draw on microscopic observations and SEM-BSE-EDS results, secondary hypogene genesis for some of bornite and chalcopyrite as a hypogene enrichment evidence. Observations from relogging show that potassic alteration has a relatively good preservation in the center of the deposit from depth to surface, but affected by intense overprinting of subsequent alterations towards margins. Evident function of ore-leaching at margins, also elevated copper grades in central parts of the deposit strongly suggest leaching-fixation mechanism. Where buffer potential of the rock is preserved copper fixation and where it totally eliminated almost complete leaching of copper happened. Consequently, we introduce leaching-fixation as index processes in hypogene enrichment at the case study. We suggest that identifying the nature of hypogene enrichment processes and its characterizations not only improve understanding about PCD's hydrothermal evolution, but also achieve exploration indicators, furthermore, industrial benefits in the production line.
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The Daisy Creek prospect, located approximately 25 km north of Thompson FaIIs, Montana, consists of stratabound Cu-Pb-Ag mineralization hosted by Helikian quartzites of the Bonner Formation, Belt Supergroup. Hypogene mineralization occurs in zones containing disseminated galena, chalcopyrite, argentiferous bornite, and argentiferous chalcocite, which precipiUted during middle diagenesis within apatite-rich, medium-grained, channel-facies quartzites. Oxidation of these sulfides occurred in two episodes, one during diagenesis under conditions of relatively low CO2 and high Ba2+ activiry, and the other during supergene weathering under conditioas ef higher CO2 and lower Ba2+ activity. In the copper zones, cupriferous goethite, acanthite and barite occur as products of diagenetic oxidation, whereas nativ€ silver, limonite and malachite occur as products of supergene weathering. ln tle lead-rich zone, diagenetic barite replaces galena, and hinsdalite @b,Sr)Al3POaSOa(OH)e, a raxe supergene mineral, fills vugs and locally replaces supergene cenrssite and pyromorphite where the lead zone overlaps P-anomalous strata.
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