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Geology and genesis of the giant pulang porphyry Cu-Au District, Yunnan, Southwest China

Citation

Cao, K and Yang, ZM and Mavrogenes, J and White, NC and Xu, JF and Li, Y and Li, WK, Geology and genesis of the giant pulang porphyry Cu-Au District, Yunnan, Southwest China, Economic Geology, 114, (2) pp. 275-301. ISSN 0361-0128 (2019) [Refereed Article]

Copyright Statement

2019 Society of Economic Geologists, Inc.

DOI: doi:10.5382/econgeo.2019.4631

Abstract

The giant Pulang porphyry Cu-Au district (446.8 million tonnes at 0.52% Cu and 0.18 g/tonne Au) is in the southern segment of the Yidun arc (Zhongdian arc), part of the Sanjiang Tethyan orogenic belt in southwest China. The district consists of three deposits: South Pulang (similar to 96% of the total ore reserves) and the smaller East and North Pulang deposits. Four intrusive phases host the three Pulang deposits, which are, in order of emplacement, premineralization fine-grained quartz diorite and coarse-grained quartz diorite, intermineralization quartz monzonite, and late-mineralization diorite porphyry. The complex intruded carbonaceous rocks of the Late Triassic Tumugou slates. Zircon U-Pb laser ablation-inductively coupled plasma-mass spectrometry dating shows that intrusive activity occurred at about 216 +/- 2 Ma.

Hydrothermal alteration of the intrusions at Pulang includes five main types: K-silicate, epidote-chlorite, chlorite-illite, quartz-illite, and clay alteration. K-silicate alteration, subdivided into early K-feldspar alteration and late biotite alteration (dominant), mainly affected the central quartz monzonite and adjacent coarse-grained quartz diorite and fine-grained quartz diorite. Epidote-chlorite alteration, the most widespread alteration in the district, extends from the deposit core outward and has overprinted K-silicate alteration at South and North Pulang. Late chlorite-illite, quartz-illite, and clay alteration have overprinted preexisting K-silicate and epidotechlorite alteration assemblages and are locally developed in all four intrusive phases. Copper and gold are positively correlated and are mainly (90%) associated with epidote-chlorite alteration and, to a lesser degree, with K-silicate and chlorite-illite alteration. Hypogene pyrrhotite is intergrown with chalcopyrite and mainly occurs in chlorite-illite- and quartz-illite-altered, coarse-grained quartz diorite at East Pulang. Molybdenite Re-Os dating shows that mineralization in the district occurred at 216.54 +/- 0.87 to 216.13 +/- 0.86 Ma.

The sequence of intrusion emplacement, alteration and veining, and sulfide associations at the three deposits suggests that South and North Pulang are two separate porphyry Cu-Au deposits, whereas East Pulang is probably a distal part of South Pulang. The dominance of primary magnetite over ilmenite and the assemblage titanite + magnetite + quartz in the causative quartz monzonite, and the abundant hydrothermal anhydrite veins associated with early K-silicate and main-mineralization epidote-chlorite alteration indicate the oxidized nature of the felsic intrusion and resultant early hydrothermal fluids. Thepyrrhotite related to late chlorite-illite and quartz-illite alteration suggests local reduction due to interaction with the carbonaceous Tumugou slates. The atypical association of epidote-chlorite alteration and Cu mineralization at Pulang either is due to fluids from another porphyry deposit nearby overprinting epidote-chlorite alteration onto preexisting copper mineralization and K silicate alteration at Pulang or is the result of collapse of epidote chlorite stable fluids into the K-silicate-altered core during waning hydrothermal activity.

Item Details

Item Type:Refereed Article
Keywords:geology, Genesis of the giant, pulang porphyry
Research Division:Earth Sciences
Research Group:Geology
Research Field:Resource geoscience
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Other mineral resources (excl. energy resources)
Objective Field:Other mineral resources (excl. energy resources) not elsewhere classified
UTAS Author:White, NC (Professor Noel White)
ID Code:152221
Year Published:2019
Web of Science® Times Cited:26
Deposited By:CODES ARC
Deposited On:2022-08-15
Last Modified:2022-09-14
Downloads:0

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