Abstract
The giant Jianchaling Au (52 t Au) deposit is located in the Mian-Lue-Yang Terrane in the southern part of the Qinling Orogen of central China and is hosted by metamorphosed carbonate rocks of the Late Neoproterozoic Duantouya Formation. The deposit consists of multiple generations of mineralised quartz(-carbonate) veins in WNW-trending extensional ductile-brittle shear zones. Based on the mineral assemblages and cross-cutting relationships between the quartz(-carbonate) veins, the paragenesis is characterised by an early coarse-grained pyrite-pyrrhotite-pentlandite-dolomite-quartz assemblage (I), followed by pyrite-sphalerite-galena-carbonate-arsenopyrite-fuchsite-carbonate-quartz containing gold (II), and fine-grained pyrite-dolomite-calcite-quartz-realgar (As2S2)-orpiment (As2S3) (III). The H-O-C isotope systematics for the three vein sets indicate that the mineralising fluid is probably sourced from the metamorphic dehydration of carbonate rocks in the Duantouya Formation, and gradually mixed with meteoric water during the emplacement of the third vein set. The δ34S values for sulfides (6.3–16.6‰) from the second auriferous vein set are greater than zero, indicating sulfates reduction from the Neoproterozoic metamorphic rocks (Duantouya Fm). The (206Pb/204Pb)i ratios from pyrite (17.521–18.477) from each of the vein sets overlap those of the ultramafic rocks (18.324–18.717) and the Bikou Group (17.399–18.417), indicating that the units are possible sources for the sulfides in the mineralisation. Both εNd(t) and Isr(t) of sulfide overlap with the meta-ultramafic field and Duantouya formation and dominated with mature Sr-Nd character, which indicated that the Duantouya may play an important role during the ore formation and there may exist a minor ultramafic source that is involved in the ore fluid. The S-Pb-Sr-Nd isotopic ratios are closely related to those of the Bikou Group and Duantouya Formation, which indicates that the mineralised fluid has interacted with both units. Combining the previously published data with data from this study on the mineralised area, we surmise that Jianchaling is characteristic of an orogenic-type gold deposit related to the Triassic Qinling Orogeny associated with continental collision.
Highlights
The different tectonic events are accompanied by different types of mineralisation and associated hydrothermal alteration of different ages [1,2,3], including orogenic-Au deposits [4,5,6]
Oxygen and carbon isotopic systematics indicate that the ore-forming fluids at the Jianchaling Au deposit progressively evolved from an early stage represented by the first vein set associated with deformation and metamorphism of the country rocks
This was succeeded by a late tectonic stage represented by the mineralised second vein set sourced from a mixed metamorphic and meteoric fluid, and progressed to a late stage represented by the third vein set
Summary
The different tectonic events are accompanied by different types of mineralisation and associated hydrothermal alteration of different ages [1,2,3], including orogenic-Au deposits [4,5,6]. Many of these deposits record multiple deformation events, making difficult to study and leading to uncertainty in their genesis [7,8,9]. The genesis of the giant Jianchaling Au deposit is still poorly understood
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