Giant Sb metallogenic belt in South China: A product of Late Mesozoic flat-slab subduction of paleo-Pacific plate

Abstract

The giant Sb metallogenic belt in South China (GSMB) has been proved to provide approximately half the world’s reserves and Sb production. This metallogenic belt is tectonically located along the transition zone between the Yangtze and Cathaysia blocks, covering an area of ∼ 1900 km long and ∼ 200 km wide, with a set of large or giant Sb deposits such as the Xikuangshan, Banxi, Woxi, Qinglong, and Banpo-Banian. The Sb deposits have the following features in common: localisation in sedimentary rocks or counterpart metamorphic rocks as veins or strata, structural-tectonic control of mineralisation along the regional NE-trending faults, and the presence of intermediate-mafic dyke rocks in the belt whose relationship with Sb mineralisation is not obvious. Fluid inclusion data show that the Sb mineralisation in this belt generally occurred under low-temperature and low-salinity conditions (140–250 °C, 0.2%–10% NaClequiv.). Abundant isotope data suggest that the Sb deposits in this belt were dominantly generated by crustal fluids from the Proterozoic basement sequences and fresh meteoric water or their mixture with various proportions, whereas the magmatic contribution to Sb mineralisation in this region is a preferential heat source rather than a material supplier (i.e., fluids and metals). The reported geochronological data of representative Sb deposits suggest an age distribution trend of Sb mineralisation, from 120 to 130 Ma in the Xikuangshan, Banxi, Woxi, Banpo and Banian Sb deposits in the northern and central parts of the GSMB, to 140–165 Ma in the Qinglong, Muli and Maxiong Sb deposits in the southern part of this belt. This age trend of the GSMB is largely comparable to that of Mesozoic igneous rocks in the Cathaysia Block, indicating both of them are the products of the west-northwestward flat-slab subduction and post-subduction of the paleo-Pacific Plate during the Late Mesozoic. In combination of the geological, geochemical, and reported geochronological data, we proposed that the Sb deposits in GSMB in South China probably have been mainly generated by low-temperature and low-salinity crustal fluids which leached Sb and S from basement sequences under an extensional setting during Late Mesozoic.