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Copper, gold and silver enrichment in ore mylonites within massive sulphide orebodies at Hongtoushan VHMS deposit, N.E. China

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Gu, L and Zheng, Y and Tang, X and Zaw, K and Della-Pasqua, FN and Wu, C and Tian, Z and Lu, J and Ni, P and Li, X and Yang, F and Wang, Xiangwen (2007) Copper, gold and silver enrichment in ore mylonites within massive sulphide orebodies at Hongtoushan VHMS deposit, N.E. China. Ore Geology Reviews, 30 (1). pp. 1-29. ISSN 0169-1368

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Abstract

The Hongtoushan Archaean Cu–Zn Volcanic-hosted Massive Sulphide (VHMS) deposit occurs in the Hunbei granite–
greenstone terrane, Liaoning Province of NE China. The ores were metamorphosed (3.0–2.8 Ga) to upper amphibolite facies at
temperatures between 600 and 650 8C, and underwent three phases of deformation. The deformation has transposed the
stratiform orebodies into a Y-shaped configuration. Ore minerals in the deposit were originally composed of pyrite, pyrrhotite,
chalcopyrite and sphalerite. Prograde metamorphism obliterated almost all the sedimentary textures in the ores, and the present
ore textures were formed substantially during peak and post-peak metamorphism. Intensive remobilisations have occurred in the
Hongtoushan deposit at various scales.
There are more than 30 oreshoots inside the main massive sulphide orebodies. The oreshoots range from 2 to 30 m in length, 0.1
to 1.5 m in width, and 2 to 30 m in depth extension. Most run parallel or sub-parallel to the strike of the massive sulphide ore layers
with only a few being developed in metamorphic rocks in the immediate vicinity of the sulphide orebodies. Almost all the sulphide
and gangue minerals in the oreshoots have been affected by intense shearing. Pyrite is characterised by cataclastic flow; pyrrhotite,
chalcopyrite and sphalerite exhibit strong plasticity. Hydrothermal alteration minerals in the oreshoots are dominated by
deformation-free hornblende, actinolite, epidote, clinozoisite, biotite, muscovite, albite, carbonate and quartz. Cu, Au and Ag in
the ore mylonites average 11 wt.%, 1.74 and 235 g/t, respectively. Compared to the massive sulphide ores, these oreshoots show
remarkable enrichment of these elements with enrichment coefficients of 5.3, 5.0 and 4.6, respectively.We draw the conclusion that
these oreshoots are actually ore mylonites overprinted by late-stage fluids.
The presence of annealing textures in pyrrhotite and the absence in pyrite suggest that formation and succeeding annealing of
the ore mylonite took place over the temperature range from 550 to 450 8C. Such a temperature range, combined with the geology
and mineralogy, indicates that these ore mylonites and the derivative oreshoots were formed during upper-greenschist-facies
retrograde metamorphism. Similarity of the ore mylonites to the massive ores in metal varieties and lead isotope ages suggest that
Cu, Au and Ag of the overprinting fluids on the ore mylonites were derived mainly from the nearby massive sulphide ores.However, lead isotope compositions of the ore mylonites also suggest that an external source, such as the metamorphic host rocks,
has also contributed to their metal budget.

Item Type: Article
Keywords: Ductile shear zone; Ore mylonite; Remobilisation; Massive sulphide deposit; Retrograde metamorphism; Hongtoushan; Liaoning
Journal or Publication Title: Ore Geology Reviews
Page Range: pp. 1-29
ISSN: 0169-1368
Identification Number - DOI: 10.1016/j.oregeorev.2005.09.001
Additional Information:

The definitive version is available at http://www.sciencedirect.com

Date Deposited: 05 Jun 2008 03:30
Last Modified: 18 Nov 2014 03:42
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