Overprinting mineralization in the Paleozoic Yandong porphyry copper deposit, Eastern Tianshan, NW China-Evidence from geology, fluid inclusions and geochronology

The Yandong porphyry copper deposit is located in the southern part of the Dananhu-Tousuquan Island Arc belt in Eastern Tianshan (Xinjiang, NW China). The Dananhu-Tousuquan belt contains a number of large and medium Cu deposits, among which the Yandong deposit (similar to 2.0 Mt Cu @ 0.67%) is the largest. The Yandong Cu deposit is hosted by plagiogranite porphyry and the Carboniferous Qi'eshan Group mafic to intermediate calc-alkaline volcanic and pyroclastic rocks. According to the crosscutting relationships and mineral assemblages, the alteration and mineralization processes at Yandong comprise three episodes: the porphyry mineralization episode (including potassic, propylitic, early phyllic and late phyllic stages), the overprinting mineralization episode (including main- and post-mineralization stages) and lastly supergene alteration episode. Fluid inclusions (FIs) in quartz from the potassic, early late phyllic and post-mineralization stages, and anhydrite from the main-/post-mineralization stages include four types: 1) vapor-liquid two phases (W-type), 2) daughter mineral-bearing (S-type), 3) pure liquid (PW-type), and 4) pure vapor (PV-type). The potassic stage contains W-, S- and PV-type FIs, which yielded homogenization temperatures of 304-445 degrees C (mainly 340-400 degrees C) and salinities of 3.1-16.4 (mainly 4.0-10.0) wt% NaCl eqv. At the early phyllic stage, three types of FIs are identified, i.e., the W-, S-, and PV-type. The S-type and W-type FIs homogenized at 213-441 degrees C (mainly 280-300 degrees C) and 241-352 degrees C (mainly 300-320 degrees C), respectively, with corresponding salinities of 33.1-52.0 (mainly 34.0-40.0) wt% NaCl eqv. and 0.9-15.9 (mainly 0.9-4.0) wt% NaCl eqv., respectively. The late phyllic stage contains W-, S- and PW-type FIs, which homogenized at 146-248 degrees C (mainly 160-180 degrees C), with salinities ranging from 3.9 to 18.2 (mainly 4.0-8.0) wt% NaCl eqv. Mineralization depths calculated from FIs are: 0.8-1.2 km (Stage I), 0.6-1.8 km (Stage IIIA) and 0.4-0.7 km (Stage IIIB). Fluid boiling and mixing likely occurred during the porphyry mineralization period, leading to the precipitation of pyrite and chalcopyrite. During the overprinting mineralization, the Wand PV-type FIs occur in the main-mineralization anhydrite, with homogenization temperatures and salinities being 248-421 degrees C (mainly 300-340 degrees C) and 5.3-13.8 (mainly 8.0-10.0) wt% NaCl eqv., respectively. The post-mineralization quartz and anhydrite homogenized at 105-195 degrees C (mainly 120-140 degrees C), with salinities of 0.5-13.6 (mainly 8.0-10.0) wt% NaCl eqv. The ore-forming fluids may have predominantly been entrapped at 0.8-1.6 km (Stage IV) and 0.3-0.6 km (Stage V). The decreasing temperature may have led to the sulfides and sulfate precipitation and enrichment. Sericite 40Ar/39Ar dating of the altered plagiogranite porphyry yielded a plateau age of 332.8 +/- 3.8 Ma, consistent with the age of the early ore-forming plagiogranite porphyry (339-332 Ma). Re-Os dating of molybdenite, coexisting with chalcopyrite-anhydrite-chlorite-calcite assemblage, yielded an age of 324.3 +/- 2.7 Ma (weighted mean), consistent with the late quartz albite porphyry age (zircon U-Pb: 323.6 +/- 2.5 Ma). Consequently, we propose that at least two mineralization episodes may have occurred at Yandong, with the second episode contributing to the majority of the Cu-Mo resources. Such overprinting mineralization style at Yandong may represent a good example of the Paleozoic Cu deposits in the Central Asian Orogenic Belt. (C) 2017 Elsevier B.V. All rights reserved. The Yandong porphyry copper deposit is located in the southern part of the Dananhu-Tousuquan Island Arc belt in Eastern Tianshan (Xinjiang, NW China). The Dananhu-Tousuquan belt contains a number of large and medium Cu deposits, among which the Yandong deposit (similar to 2.0 Mt Cu @ 0.67%) is the largest. The Yandong Cu deposit is hosted by plagiogranite porphyry and the Carboniferous Qi'eshan Group mafic to intermediate calc-alkaline volcanic and pyroclastic rocks. According to the crosscutting relationships and mineral assemblages, the alteration and mineralization processes at Yandong comprise three episodes: the porphyry mineralization episode (including potassic, propylitic, early phyllic and late phyllic stages), the overprinting mineralization episode (including main- and post-mineralization stages) and lastly supergene alteration episode. Fluid inclusions (FIs) in quartz from the potassic, early late phyllic and post-mineralization stages, and anhydrite from the main-/post-mineralization stages include four types: 1) vapor-liquid two phases (W-type), 2) daughter mineral-bearing (S-type), 3) pure liquid (PW-type), and 4) pure vapor (PV-type). The potassic stage contains W-, S- and PV-type FIs, which yielded homogenization temperatures of 304-445 degrees C (mainly 340-400 degrees C) and salinities of 3.1-16.4 (mainly 4.0-10.0) wt% NaCl eqv. At the early phyllic stage, three types of FIs are identified, i.e., the W-, S-, and PV-type. The S-type and W-type FIs homogenized at 213-441 degrees C (mainly 280-300 degrees C) and 241-352 degrees C (mainly 300-320 degrees C), respectively, with corresponding salinities of 33.1-52.0 (mainly 34.0-40.0) wt% NaCl eqv. and 0.9-15.9 (mainly 0.9-4.0) wt% NaCl eqv., respectively. The late phyllic stage contains W-, S- and PW-type FIs, which homogenized at 146-248 degrees C (mainly 160-180 degrees C), with salinities ranging from 3.9 to 18.2 (mainly 4.0-8.0) wt% NaCl eqv. Mineralization depths calculated from FIs are: 0.8-1.2 km (Stage I), 0.6-1.8 km (Stage IIIA) and 0.4-0.7 km (Stage IIIB). Fluid boiling and mixing likely occurred during the porphyry mineralization period, leading to the precipitation of pyrite and chalcopyrite. During the overprinting mineralization, the Wand PV-type FIs occur in the main-mineralization anhydrite, with homogenization temperatures and salinities being 248-421 degrees C (mainly 300-340 degrees C) and 5.3-13.8 (mainly 8.0-10.0) wt% NaCl eqv., respectively. The post-mineralization quartz and anhydrite homogenized at 105-195 degrees C (mainly 120-140 degrees C), with salinities of 0.5-13.6 (mainly 8.0-10.0) wt% NaCl eqv. The ore-forming fluids may have predominantly been entrapped at 0.8-1.6 km (Stage IV) and 0.3-0.6 km (Stage V). The decreasing temperature may have led to the sulfides and sulfate precipitation and enrichment. Sericite 40Ar/39Ar dating of the altered plagiogranite porphyry yielded a plateau age of 332.8 +/- 3.8 Ma, consistent with the age of the early ore-forming plagiogranite porphyry (339-332 Ma). Re-Os dating of molybdenite, coexisting with chalcopyrite-anhydrite-chlorite-calcite assemblage, yielded an age of 324.3 +/- 2.7 Ma (weighted mean), consistent with the late quartz albite porphyry age (zircon U-Pb: 323.6 +/- 2.5 Ma). Consequently, we propose that at least two mineralization episodes may have occurred at Yandong, with the second episode contributing to the majority of the Cu-Mo resources. Such overprinting mineralization style at Yandong may represent a good example of the Paleozoic Cu deposits in the Central Asian Orogenic Belt. (C) 2017 Elsevier B.V. All rights reserved. The Yandong porphyry copper deposit is located in the southern part of the Dananhu-Tousuquan Island Arc belt in Eastern Tianshan (Xinjiang, NW China). The Dananhu-Tousuquan belt contains a number of large and medium Cu deposits, among which the Yandong deposit (similar to 2.0 Mt Cu @ 0.67%) is the largest. The Yandong Cu deposit is hosted by plagiogranite porphyry and the Carboniferous Qi'eshan Group mafic to intermediate calc-alkaline volcanic and pyroclastic rocks. According to the crosscutting relationships and mineral assemblages, the alteration and mineralization processes at Yandong comprise three episodes: the porphyry mineralization episode (including potassic, propylitic, early phyllic and late phyllic stages), the overprinting mineralization episode (including main- and post-mineralization stages) and lastly supergene alteration episode. Fluid inclusions (FIs) in quartz from the potassic, early late phyllic and post-mineralization stages, and anhydrite from the main-/post-mineralization stages include four types: 1) vapor-liquid two phases (W-type), 2) daughter mineral-bearing (S-type), 3) pure liquid (PW-type), and 4) pure vapor (PV-type). The potassic stage contains W-, S- and PV-type FIs, which yielded homogenization temperatures of 304-445 degrees C (mainly 340-400 degrees C) and salinities of 3.1-16.4 (mainly 4.0-10.0) wt% NaCl eqv. At the early phyllic stage, three types of FIs are identified, i.e., the W-, S-, and PV-type. The S-type and W-type FIs homogenized at 213-441 degrees C (mainly 280-300 degrees C) and 241-352 degrees C (mainly 300-320 degrees C), respectively, with corresponding salinities of 33.1-52.0 (mainly 34.0-40.0) wt% NaCl eqv. and 0.9-15.9 (mainly 0.9-4.0) wt% NaCl eqv., respectively. The late phyllic stage contains W-, S- and PW-type FIs, which homogenized at 146-248 degrees C (mainly 160-180 degrees C), with salinities ranging from 3.9 to 18.2 (mainly 4.0-8.0) wt% NaCl eqv. Mineralization depths calculated from FIs are: 0.8-1.2 km (Stage I), 0.6-1.8 km (Stage IIIA) and 0.4-0.7 km (Stage IIIB). Fluid boiling and mixing likely occurred during the porphyry mineralization period, leading to the precipitation of pyrite and chalcopyrite. During the overprinting mineralization, the Wand PV-type FIs occur in the main-mineralization anhydrite, with homogenization temperatures and salinities being 248-421 degrees C (mainly 300-340 degrees C) and 5.3-13.8 (mainly 8.0-10.0) wt% NaCl eqv., respectively. The post-mineralization quartz and anhydrite homogenized at 105-195 degrees C (mainly 120-140 degrees C), with salinities of 0.5-13.6 (mainly 8.0-10.0) wt% NaCl eqv. The ore-forming fluids may have predominantly been entrapped at 0.8-1.6 km (Stage IV) and 0.3-0.6 km (Stage V). The decreasing temperature may have led to the sulfides and sulfate precipitation and enrichment. Sericite 40Ar/39Ar dating of the altered plagiogranite porphyry yielded a plateau age of 332.8 +/- 3.8 Ma, consistent with the age of the early ore-forming plagiogranite porphyry (339-332 Ma). Re-Os dating of molybdenite, coexisting with chalcopyrite-anhydrite-chlorite-calcite assemblage, yielded an age of 324.3 +/- 2.7 Ma (weighted mean), consistent with the late quartz albite porphyry age (zircon U-Pb: 323.6 +/- 2.5 Ma). Consequently, we propose that at least two mineralization episodes may have occurred at Yandong, with the second episode contributing to the majority of the Cu-Mo resources. Such overprinting mineralization style at Yandong may represent a good example of the Paleozoic Cu deposits in the Central Asian Orogenic Belt. (C) 2017 Elsevier B.V. All rights reserved. The Yandong porphyry copper deposit is located in the southern part of the Dananhu-Tousuquan Island Arc belt in Eastern Tianshan (Xinjiang, NW China). The Dananhu-Tousuquan belt contains a number of large and medium Cu deposits, among which the Yandong deposit (similar to 2.0 Mt Cu @ 0.67%) is the largest. The Yandong Cu deposit is hosted by plagiogranite porphyry and the Carboniferous Qi'eshan Group mafic to intermediate calc-alkaline volcanic and pyroclastic rocks. According to the crosscutting relationships and mineral assemblages, the alteration and mineralization processes at Yandong comprise three episodes: the porphyry mineralization episode (including potassic, propylitic, early phyllic and late phyllic stages), the overprinting mineralization episode (including main- and post-mineralization stages) and lastly supergene alteration episode. Fluid inclusions (FIs) in quartz from the potassic, early late phyllic and post-mineralization stages, and anhydrite from the main-/post-mineralization stages include four types: 1) vapor-liquid two phases (W-type), 2) daughter mineral-bearing (S-type), 3) pure liquid (PW-type), and 4) pure vapor (PV-type). The potassic stage contains W-, S- and PV-type FIs, which yielded homogenization temperatures of 304-445 degrees C (mainly 340-400 degrees C) and salinities of 3.1-16.4 (mainly 4.0-10.0) wt% NaCl eqv. At the early phyllic stage, three types of FIs are identified, i.e., the W-, S-, and PV-type. The S-type and W-type FIs homogenized at 213-441 degrees C (mainly 280-300 degrees C) and 241-352 degrees C (mainly 300-320 degrees C), respectively, with corresponding salinities of 33.1-52.0 (mainly 34.0-40.0) wt% NaCl eqv. and 0.9-15.9 (mainly 0.9-4.0) wt% NaCl eqv., respectively. The late phyllic stage contains W-, S- and PW-type FIs, which homogenized at 146-248 degrees C (mainly 160-180 degrees C), with salinities ranging from 3.9 to 18.2 (mainly 4.0-8.0) wt% NaCl eqv. Mineralization depths calculated from FIs are: 0.8-1.2 km (Stage I), 0.6-1.8 km (Stage IIIA) and 0.4-0.7 km (Stage IIIB). Fluid boiling and mixing likely occurred during the porphyry mineralization period, leading to the precipitation of pyrite and chalcopyrite. During the overprinting mineralization, the Wand PV-type FIs occur in the main-mineralization anhydrite, with homogenization temperatures and salinities being 248-421 degrees C (mainly 300-340 degrees C) and 5.3-13.8 (mainly 8.0-10.0) wt% NaCl eqv., respectively. The post-mineralization quartz and anhydrite homogenized at 105-195 degrees C (mainly 120-140 degrees C), with salinities of 0.5-13.6 (mainly 8.0-10.0) wt% NaCl eqv. The ore-forming fluids may have predominantly been entrapped at 0.8-1.6 km (Stage IV) and 0.3-0.6 km (Stage V). The decreasing temperature may have led to the sulfides and sulfate precipitation and enrichment. Sericite 40Ar/39Ar dating of the altered plagiogranite porphyry yielded a plateau age of 332.8 +/- 3.8 Ma, consistent with the age of the early ore-forming plagiogranite porphyry (339-332 Ma). Re-Os dating of molybdenite, coexisting with chalcopyrite-anhydrite-chlorite-calcite assemblage, yielded an age of 324.3 +/- 2.7 Ma (weighted mean), consistent with the late quartz albite porphyry age (zircon U-Pb: 323.6 +/- 2.5 Ma). Consequently, we propose that at least two mineralization episodes may have occurred at Yandong, with the second episode contributing to the majority of the Cu-Mo resources. Such overprinting mineralization style at Yandong may represent a good example of the Paleozoic Cu deposits in the Central Asian Orogenic Belt. (C) 2017 Elsevier B.V. All rights reserved.