The geology and mineralisation of Coppermine Island
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Abstract Folded Mesozoic quartzo-feldspathic sandstones and siltstones have been intruded and hornfelsed by small Miocene? stocks of diorite, quartz diorite, and granodiorite, and by numerous dikes of quartz andesite and dacite. The dikes intrude both the metasedimentary and plutonic rocks and radiate from an area now occupied by an explosion breccia pipe. Pyrrhotite-pyrite-chalcopyrite mineralisation occurs in two environments, (a) along closely spaced joints in a fine grained pyroxene diorite, where it is associated with secondary amphibole and biotite alteration, and (b) between fragments in the breccia pipe where it is associated with chlorite, adularia, sericite, calcite, epidote, and quartz alteration. In both environments permeability of host rocks was important in localising the sulphide mineralisation and hydrothermal alteration, both of which post-date the injection of the dikes. Hydrothermal fluids are thought to have originated from the deeper seated equivalents of the hypabyssal rocks. Preliminary sampling and geological mapping suggest that the copper ore reserves on Coppermine Island are, (a) certain—500,000 tons, (b) probable—8,000,000 tons, and (c) maximum possible—30,000,000 tons. The grade of the mineralisation is estimated to be approximately 0–5% Cu.Keywords:
Diorite
Sericite
Breccia
Dike
Dacite
Country rock
Pyroxene
Yandong large-size porphyry copper deposit is located in the Late Paleozoic Dananhu island arc in Eastern Tianshan,Xinjiang.Lower Carboniferous Qi'eshan Group occurred in the Yandong region.New results recognize a volcanic apparatus at Yandong that includes two cycles comprising five lithofacies.The first cycle consists of the effusive(basalt and andesite),explosive(auto-brecciated lava)and pyroclastic phases(tuff).The second cycle is characterized by the intermediate and felsic intrusions.The intrusions,including the diorite porphyry,aplite diorite and plagiogranite porphyry,are ore-bearing intrusions.Both diorite porphyry(including aplite diorite)and plagiogranite porphyry host the bulk of the copper mineralization at Yandong and have been overprinted by the two distinct alteration systems.Diorite porphyry has been overprinted by three alteration assemblages,including the central sericite-chlorite assemblage and chlorite-sericite assemblage and distal propylitic assemblage.Cu-Fe sulfides are closely associated with the sericite-chlorite assemblage.Plagiogranite porphyry,cutting the early-stage diorite porphyry,has undergone the central phyllic and surrounding strong and weak sericite alteration.Intense phyllic alteration produced the high-grade copper ore at Yandong.The two alteration systems at Yandong were characterized by rare potassic alteration and widespread sericite alteration.
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This study focuses on mapping hydrothermal alterations in Musina Copper Deposit Field which is characterized by unique concentric zonation of hydrothermal alterations from an outer zone of sericitization (phyllic) followed by inward zones of chloritization and epidotization (propylitic). Per-pixel and mixture tuned matched filtering (MTMF) sub-pixel unmixing methods were applied on ASTER data to map hydrothermal alterations. False colour composite (FCC) generated from combination of propylitic, phyllic and host rock index was effective in delineating alteration zones. The spatial distribution of alteration group minerals: chlorite–epidote and sericite–muscovite from MTMF classification correspond with their associated alteration zones. Correlation coefficient (R2) was utilized to assess accuracy of the results by comparing MF scores of alteration minerals with copper concentrations. R2 was 0.78 for chlorite–epidote and 0.69 for sericite– muscovite. Copper concentration levels increase towards chlorite–epidote region which represents the inward propylitic zone. Following the geometry and alteration zonation, follow-up targets were generated.
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Abstract Petrology and P–T estimates indicate that a magmatic epidote‐bearing quartz diorite pluton from Mt. Gamsby, Coast Plutonic Complex, British Columbia, was sourced at pressures below ∼1.4 GPa and cooled nearly isobarically at ∼0.9 GPa. The P–T path indicates that the magma was within the stability field of magmatic epidote early and remained there upon final crystallization. The pluton formed and crystallized at depths greater than ∼30 km. REE data indicate that garnet was absent in the melting region and did not fractionate during crystallization. This suggests that the crust was less than or equal to ∼55 km thick at 188 Ma during the early phases of magmatism in the Coast Plutonic Complex. Late Cretaceous contractional deformation and early Tertiary extension exhumed the rocks to upper crustal levels. Textures of magmatic epidote and other magmatic phases, combined with REE data, can be important for constraining the P–T path followed by magmas.
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Abstract Folded Mesozoic quartzo-feldspathic sandstones and siltstones have been intruded and hornfelsed by small Miocene? stocks of diorite, quartz diorite, and granodiorite, and by numerous dikes of quartz andesite and dacite. The dikes intrude both the metasedimentary and plutonic rocks and radiate from an area now occupied by an explosion breccia pipe. Pyrrhotite-pyrite-chalcopyrite mineralisation occurs in two environments, (a) along closely spaced joints in a fine grained pyroxene diorite, where it is associated with secondary amphibole and biotite alteration, and (b) between fragments in the breccia pipe where it is associated with chlorite, adularia, sericite, calcite, epidote, and quartz alteration. In both environments permeability of host rocks was important in localising the sulphide mineralisation and hydrothermal alteration, both of which post-date the injection of the dikes. Hydrothermal fluids are thought to have originated from the deeper seated equivalents of the hypabyssal rocks. Preliminary sampling and geological mapping suggest that the copper ore reserves on Coppermine Island are, (a) certain—500,000 tons, (b) probable—8,000,000 tons, and (c) maximum possible—30,000,000 tons. The grade of the mineralisation is estimated to be approximately 0–5% Cu.
Diorite
Sericite
Breccia
Dike
Dacite
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Pyroxene
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