SU Yan1, LIU Feng-xiang2, LI Yu-hua2*, DENG Ming-guo1
(1. School of Land and Resources Engineering, Kunming University of Science and Technology, Kunming 650093, China;
2. No.209 Geological Team of Yunnan Nuclear Industry, Kunming 650032, China)
Abstract: The Qingyangchang vein type Cu-Co polymetallic deposit is the latest achievement of the exploration in the southwestern Lanping basin in recent years. The ore bodies occurred in the dark purple sandstone of the Mesozoic Upper Jurassic Bazhulu Formation (J3b) . However, many geological characteristics of this deposit are obviously different from those of the typical sandstone type (SSC) Cu deposits. The fault structures are developed in the deposit. h Two groups of faults, NW- and NE-trending, are distributed in form of interweaved framework in the deposit area. The ore bodies occurred mainly in forms of veins and lens in NE-trending tensile fracture zones. The deposit has a large number of ore bodies (up to16), which are characterized with relatively large thickness (up to 14.87 m), large extension length (up to 652 m for the KT1 orebody), steep angle (60°－80°), high Cu grade (average 2.01%), and associated Co (0.027%) and Ag (36.29 g/t) of ores. The geological process of deposit can be divided into sedimentary diagenetic stage, hydrothermal ore-forming stage, and supergene stage. The hydrothermal mineralization stage is further divided into four phases including PhaseⅠ (siderite-chalcopyrite-barite), Phase Ⅱ (tennantite-chalcopyrite-siderite), Phase Ⅲ (tennantite-siderite), and Phase Ⅳ (barite-siderite-tennantite), with hydrothermal mineral assemblages of major tennantite, barite, siderite, chalcopyrite, pyrite and minor chalcocite, galena, bismuthinite, arsenopyrite, quartz, and carbonates. The ores are characterized with subhedral-anhedral replacement, exsolution, skeletal, and replacement rim textures and commonly typical hydrothermal structures such as brecciated, massive, veining, stockwork veining, banded, and miarolitic structures. The ore bodies occurred in the obvious discoloration altered structural fractured zone, with the wall rock alterations of baritization, sideritization, and weak silicification. Geological characteristics of the deposit show that shapes of ore bodies, textures and structures of ores, mineralization and enrichment characteristics of the deposit are all closely related to the faults, joints, and fissures in the area. The rare earth elements analysis shows that barites of different ore-forming stages have characteristics of low total REE contents which are changed in a small range, and the MREE-enriched "W" type distribution patterns with positive Eu anomalies (δEu = 18.99－24.32) and the negative Ce anomalies (δCe = 0.1－0.14). It suggests that the ore-forming fluid could be sourced from the basin hot brine and the ore-forming materials could be mainly sourced from strata (especially the salt-bearing strata). In this paper, on the basis of the analysis of regional metallogenic geological background, and detailed study of the deposit geology, ore deposit (ore bodies) characteristics, ore textures and structures, wall rock alteration, and geochemical characteristics of rare earth elements of the deposit, we have suggested that the Qingyangchang deposit was formed in close relationship with the thrust-nappe structures in process of the Cenozoic tectonic evolution of the Lanping basin, and it was a product of the large-scale mineralization caused by the continent-continenta collision orogenic event.
Keywords: Lanping basin; the Qingyangchang vein type Cu-Co deposit; geological features; rare earth elements; genesis of the deposit; prospecting indicators
ACTA MINERALOGICA SINICA Vol. 40, No.5, 2020, page 615-627
