An overview of timing and structural geometry of gold, gold-antimony and antimony mineralization in the Jiangnan Orogen, southern China

Abstract

The Jiangnan Orogen, located between the Yangtze and Cathaysia Blocks in southern China, hosts significant gold and antimony resources. Long-standing controversies over the number and precise timing of gold, gold-antimony and antimony mineralization event(s), and the genesis of these deposits, limit the understanding and exploration of this giant gold and antimony system. Together with geological evidence, a critical review of the published geochronological data of these deposits suggest that there were two gold events in the Triassic (~235 Ma) and Early Cretaceous (~142–130 Ma), two gold-antimony events in the Early Devonian (~402 Ma) and Late Triassic-Middle Jurassic (~224–163 Ma: possibly equivalent to the two gold events), and one antimony event in the Early Cretaceous (~130 Ma). There are other possible gold events in the Neoproterozoic or at an even older age, and Ordovician to Early Devonian, which are constrained only by limited geological evidence and a few non-robust isotopic ages. The regional distribution of the gold, gold-antimony and antimony districts, and deposits therein, reveal a first-order control on the mineralization by crustal scale faults which acted as ore-forming fluid pathways connected to deep fluid and metal source areas. Second- and third-order faults that are situated along the jogs of the first-order faults, especially fault corridors defined by NNE-NE-trending second-order faults and third-order NW to E-W-trending discontinuous oblique faults, provided favorable locations for Pre-Cretaceous gold-(antimony) mineralization. In addition, NE-trending open anticlines, linked to deep crustal levels by first-order faults, host significant antimony and minor gold mineralization, and the curvilinear Fanjingshan detachment Fault hosts some gold and antimony deposits. Locally, at deposit to orebody-scales, pre-ore barren quartz veins and magmatic dikes were the loci for mineralization in some gold-antimony deposits. The structural geometry of the pre-Cretaceous gold and gold-antimony deposits suggests an Early Devonian orogenic gold-antimony mineralization event during a transpressional tectonic regime related to coeval intracontinental orogeny between the Yangtze and Cathaysian Blocks. In contrast, Triassic orogenic gold and Triassic-Middle Jurassic orogenic gold-antimony events are interpreted to relate to distal effects of the collision between the North and South China blocks. The structurally-contrasting major Early Cretaceous epizonal antimony mineralization event, together with contemporaneous hydrothermal gold mineralization, is interpreted to have been controlled by normal faults and pre-ore open folds in an extensional tectonic regime related to the distal effects of rollback of the paleo-Pacific Plate after ~135 Ma. For future geoscience-based exploration in the Orogen, documentation and interpretation of critical structural geometries of gold, gold-antimony and antimony deposits is a vital step towards successful target generation.