Overprinting mineralization in the Paleozoic Yandong porphyry copper deposit, Eastern Tianshan, NW China-Evidence from geology, fluid inclusions and geochronology
|dc.identifier.citation||Wang, Y. and Chen, H. and Xiao, B. and Han, J. and Fang, J. and Yang, J. and Jourdan, F. 2016. Overprinting mineralization in the Paleozoic Yandong porphyry copper deposit, Eastern Tianshan, NW China-Evidence from geology, fluid inclusions and geochronology. Ore Geology Reviews. 100: pp. 148-167.|
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 (~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. °C (mainly 340-400. °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. °C (mainly 280-300. °C) and 241-352. °C (mainly 300-320. °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. °C (mainly 160-180. °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 W- and PV-type FIs occur in the main-mineralization anhydrite, with homogenization temperatures and salinities being 248-421. °C (mainly 300-340. °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. °C (mainly 120-140. °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±3.8Ma, consistent with the age of the early ore-forming plagiogranite porphyry (339-332Ma). Re-Os dating of molybdenite, coexisting with chalcopyrite-anhydrite-chlorite-calcite assemblage, yielded an age of 324.3±2.7Ma (weighted mean), consistent with the late quartz albite porphyry age (zircon U-Pb: 323.6±2.5Ma).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.
|dc.publisher||Elsevier Science BV|
|dc.title||Overprinting mineralization in the Paleozoic Yandong porphyry copper deposit, Eastern Tianshan, NW China-Evidence from geology, fluid inclusions and geochronology|
|dcterms.source.title||Ore Geology Reviews|
|curtin.department||Department of Applied Geology|
|curtin.accessStatus||Fulltext not available|
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