Geological Characteristics and Genesis of the Jiamoshan MVT Pb–Zn Deposit in the Sanjiang belt, Tibetan Plateau

Abstract

The carbonate‐hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust‐fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst‐controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore‐forming fluids belonged to a Mg2+–Na+–K+–SO42––Cl−–F−–NO3−–H2O system at low temperatures (120–130°C) but with high salinities (19–22% NaCl eq.). We have recognized basinal brine as the source of the ore‐forming fluids on the basis of their H–O isotopic compositions (–145‰ to –93‰ for δDV‐SMOW and –2.22‰ to 13.00‰ for δ18Ofluid), the ratios of Cl/Br (14–1196) and Na/Br (16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite (–5.0‰ to 3.7‰ for δ13CV‐PDB and 15.1‰ to 22.3‰ for δ18OV‐SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34S values are low in the galena (–3.2‰ to 0.6‰) but high in the barite (27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo‐seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples (18.3270–18.3482 for 206Pb/204Pb, 15.6345–15.6390 for 207Pb/204Pb, and 38.5503–38.5582 for 208Pb/204Pb) are similar to those of the regional Triassic volcanic‐arc rocks that formed during the closure of the Paleo‐Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.

Geology and metallogenesis of the Tiegelongnan Cu–Au–Ag deposit, Duolong ore district, Tibet

“…The Qinghai–Tibet Plateau is the highest plateau in the world, for which reason it is commonly known as the ‘roof of the world’, with a complex tectonic evolutionary history. Based on different locations, geological backgrounds and mineralization types, the Qinghai–Tibet Plateau can be divided into four major metallogenic zones from north to south, that is, the Bangong Co‐Nujiang Fe–Cu–Au–Cr Metallogenic Belt (BNMB), the Gangdese Cu–Mo–Au–Pb–Zn Metallogenic Belt (GDMB), the Northern Himalayan Sb–Au–Cr–Pb–Zn Metallogenic Belt (NHMB) and the South‐western Sanjiang Cu–Mo–Au–Ag (Pb‐Zn) Metallogenic Belt (SJMB) (Figure 1a) (Chen et al, 2006; Huang et al, 2021; Lang et al, 2020; Y. C. Liu et al, 2020; X. H. Wang et al, 2022; Zhao et al, 2020). The BNMB, located in the central part of the Qinghai–Tibet Plateau, has been the location of great breakthroughs in mineral prospecting in the past few years, amongst which the Duolong porphyry‐epithermal copper‐gold ore cluster is the most prominent one.…”

The Content Level, Spatial and Temporal Distribution Characteristics, and Health-Risk Assessment of Trace Elements in Upper Lancang River (Changdu Section)

“…Zhaqu mainly contains Jurassic purple red sand and mudstone mixed with limestone [22,23]. Changdu is an important part of the Southwest Sanjiang Pb-Zn-Cu-Ag metallogenic belt [24]. In the region, a large number of Pb-zinc deposits have been produced in carbonate rocks, and depositional mercury, antimony, arsenic, and lead-zinc deposits occur [25].…”

Stable Isotopes and Halogen Geochemistry of the Huayuan Carbonate‐hosted Pb‐Zn Ore District, South China: Implications for the Salt Source of Ore‐forming Fluids

“…In contrast, the brine generated from the dissolution of halite has been depleted of Br, which results in the high Na/Br and Cl/Br ratios of the ore-forming fluid. Some researchers have investigated these features by plotting Na and Cl versus Br and by plotting molar ratios of Na/Br versus Cl/Br (Gleeson and Turner, 2007;Engle and Rowan, 2013;Liu et al, 2020). The ore-forming fluids in the Huayuan Pb-Zn district have Cl/Br and Na/Br molar ratios of 118-384 and 39-184, respectively.…”