Abstract
The Huanxiangwa deposit is a major gold deposit in the Xiong’ershan district, which is the third-largest gold-producing district in China. Pyrites from the Huanxiangwa deposit were investigated using ore microscopy and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Pyrite is the dominant Au-bearing mineral in the Huanxiangwa deposit and can be divided into two types: medium- to fine-grained subhedral-anhedral pyrite (Py1) disseminated in altered rocks and coarse-grained subhedral-euhedral pyrite (Py2) hosted in auriferous quartz veins. LA-ICP-MS time-resolved depth profiles show that invisible gold occurs primarily as solid solution or as homogeneously distributed nanoparticles of native gold, electrum, or Au-Ag-Te minerals in Py1, whereas it is present mainly as nano- to submicron-sized inclusions of complex Au-Ag-Cu-Pb-Zn domains in Py2. The presented data indicate that the Huanxiangwa deposit resulted from two episodes of hydrothermal mineralization associated with two distinct source reservoirs. The first episode of mineralization was linked to the dehydration of deep-seated mafic-ultramafic metamorphic rock during the Triassic collision of the North China Craton with the Yangtze Craton. The second episode of mineralization was related to hydrothermal activity resulting from Early Cretaceous I-type granitic magmatism.
Highlights
The North China Craton (NCC) contains several large gold deposits and supplies almost 70% ofChina’s gold production [1,2]
Several different interpretations have been proposed, including (i) the gold deposits are of greenstone type [8], associated with the occurrence of Neoarchean high-grade metamorphic rocks that provided the source material for the metallogenesis [2]; (ii) the deposits are orogenic gold deposits that formed during a Mesozoic continental collision regime, with the gold-mineralizing fluids originating mainly from metamorphic dehydration and mixing with meteoric water [3,5,9]; and (iii) the deposits have a late
Pyrite is the most common Au-bearing sulfide mineral in the Huanxiangwa deposit and can be divided into two types based on its morphology and the host rock type: (1) Py1 is distributed in type 1 ores and comprises medium- to fine-grained subhedral-anhedral pyrite with sizes of 20–300 μm (Figure 3a,b) and (2) Py2 is found in type 2 ores and occurs as aggregates dispersed in quartz veins, consisting of coarse-grained, subhedral-euhedral crystals with a cubic or pyritohedral form that typically exceed 500 μm in diameter (Figure 3d–f)
Summary
The North China Craton (NCC) contains several large gold deposits and supplies almost 70% of. Most of the gold deposits in the Xiong’ershan area are located to the north of the Machaoying Fault and are hosted in Neoarchean metamorphic rocks and late Paleoproterozoic volcanic rocks (Figure 1b). These deposits have been extensively studied during the last two decades [3,5,6,7], but their genesis remains controversial. The characteristics of the deposits in this ore district are the deposits in this district are favorable for investigating the distribution of invisible gold infavorable pyrite.
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