川南早三叠世砂页岩型铜矿床沉积环境、成矿模式及对峨眉山地幔柱成矿系统的补充

Sedimentary environment and metallogenic model of Early Triassic sandstoneshale-hosted copper deposits in southern Sichuan and its supplement to Emeishan mantle plume metallogenic system

峨眉山地幔柱一直以来是国内外学者的研究热点之一,近年来对峨眉山地幔柱的成矿效应的关注度持续升高,但对提供成矿物源的矿床类型研究较少,特别是对砂页岩型铜矿的研究极少,砂页岩型铜矿稳定分布在沐川西部及西南部的飞仙关组底部,以往开展了大量的勘查工作,取得了较好的找矿成果,但其成矿物质来源还有较大争议。为厘清沐川地区飞仙关组底部砂页岩型铜矿床的富集规律、沉积环境和成因机制,本研究开展了野外实地调查、矿物学、岩相古地理与岩石地球化学等系统性研究,探讨其物源、富集规律、沉积环境,建立了成矿模式。研究结果表明,沐川地区砂页岩型铜矿体产出于早三叠世飞仙关组底部的一套灰绿色细碎屑岩中,主要矿石类型有粉砂质条带黏土岩型铜矿、泥质条带粉砂岩型铜矿、粉砂岩型铜矿和细砂岩型铜矿,矿石矿物以黄铜矿、斑铜矿、辉铜矿为主;沐川地区飞仙关组底部的沉积相属于有障壁型海岸相潮坪亚相,可识别出潮上泥坪微相、潮间混合坪微相、潮下砂坪微相和潮渠微相4种微相,Cu元素主要富集于粉砂质条带黏土岩和泥质条带粉砂岩等水动力条件较弱的潮间混合坪微相中,铜的富集严格受岩相古地理及沉积相的控制;Cu元素主要来源于峨眉山高钛玄武岩,西部的康滇古陆是主要的物源区;沐川地区飞仙关组底部砂页岩型铜矿属同生沉积型矿床,其成矿模式可分为峨眉山玄武岩喷溢(矿源层形成)阶段、风化剥蚀搬运阶段、沉积富集阶段和成岩保存阶段。上述成果,对西南地区进一步实现战略性矿产找矿突破和补充完善峨眉山地幔柱成矿系统具有重要意义。

The Emeishan mantle plume has always been one of the research hotspots of scholars at home and abroad.Increasing attention to the metallogenic effect of the Emeishan mantle plume in recent years,but there are few studies on the types of deposits providing metallogenic sources,in particular,there are very few studies on sandstone-shale-hosted copper deposits.Sandstone-shale-hosted copper deposits are stably distributed at the bottom of the Feixianguan Formation in the West and Southwest of Muchuan.In the past,a lot of exploration work has been carried out and good prospecting results have been achieved,but ore-forming material sources is still controversial.In order to clarify the enrichment regularity,sedimentary environment and genetic mechanism of the sandstone-shale-hosted copper deposit at the bottom of the Feixianguan Formation in Muchuan area,this study carried out systematic studies such as field investigation,mineralogy,lithofacies paleogeography and Lithogeochemistry,discussed its ore-forming material sources,enrichment regularity,sedimentary environment,and established metallogenic model.The results show that the sandstone-shale-hosted copper ore body in Muchuan area occurs in a set of grey-green fine clastic rocks at the bottom of the Early Triassic Feixianguan Formation.The main ore types are silty strip clay rock type copper ore,pelitic striped siltstone type copper ore,siltstone type copper ore and fine sandstone type copper ore,and the ore minerals are mainly chalcopyrite,bornite and chalcocite.The sedimentary facies at the bottom of the Feixianguan Formation in Muchuan area belongs to the tidal flat subfacies of the barrier coastal facies,which can be identified as four microfacies:Supratidal mud flat microfacies,intertidal mixed flat microfacies,subtidal sand flat microfacies and tidal channel microfacies.The copper element is mainly enriched in the intertidal mixed flat microfacies with weak hydrodynamic conditions such as silty strip clay rock and argillaceous strip siltstone.The enrichment of copper is strictly controlled by lithofacies palaeogeography and sedimentary facies.The copper element mainly comes from the Emeishan high titanium basalt,and the Kangdian Ancient Land in the west is the main provenance area.Sandstone-shale-hosted copper deposit at the bottom of the Feixianguan Formation in Muchuan area belongs to syngenetic sedimentary deposit.Its metallogenic model can be divided into four stages:Emeishan basalt flooding(source bed formation)stage,weathering and denudation stage,sedimentary enrichment stage and diagenetic preservation stage.The above results are of great significance to further realize the strategic mineral prospecting breakthrough and supplement and improve the metallogenic system of the Emeishan mantle plume in southwestern China.