| Lala copper deposit,located in middle part of passive continental rift system in western margin of the Yangtze Plate, and at the west end of Huili-Dongchuan aulacogen, also occurred in the junction of east-west trend Jinsha River fold belt and north-south trend Sichuan-Yunnan tectonic belt, is not only a large iron, copper and gold deposit clusters which is Cu-based with various useful components(such as Fe, Au, Co, Mo, REE) and have higher comprehensive value, but also China's venerated rich copper deposit. Its ore-bearing stratum is a suit of alkaline metavolcanics and Metamorphic Marine sedimentary rocks of Hekou Group in Proterozoic era. Ore rock is mainly divided into biotite schist type and imandrite type,so some scholars divided lala copper mine ore type into two types: imandrite type and biotite schist type; Ore bodies occur in their contact zone or alternate parts with banding, stratiform-like, lentoid and vein-like shape.Since 1956 geologists started geological prospecting work, mine construction and Mine production prospecting work, we accumulate a large number of related studies about geological datas and research results, but there are different viewpoints on the cause of deposit formation. In this paper, focusing on the research of mineralography characteristics of the ore to comprehensively master the ore type and its spatial distribution characteristics, mineral association, texture and structure of ores of the deposit, combined with country rock aiteration type, alteration zoning and its size in mining area, determine the formation sequence of minerals, and divide the metallogenic period and stage, to correctly understand the causes of Lala copper deposit mode providing basic information on mineralography.Through ore microscopic mineralography research in this thesis,it is confirmed the ore minerals are mainly magnetite, chalcopyrite, and pyrite, followed by molybdenite, marcasite, chalcocite, bornite, vallerite, sphalerite, ilmenite, rutile, malachite and azurite.Metal mineral combination mode include chalcopyrite+magnetite combination, chalcopyrite+pyrite+ magnetite / molybdenite combination, chalcopyrite +hematite / ilmenite + magnetite combination and pyrite + chalcopyrite + magnetite, pyrrhotite combination.In this paper,it is confirmed that ores in Lala copper deposit have complicated structures, including with idiomorphism-granular texture, hypidiomorphic granular texture, xenomorphic granular texture, metasomatic relict texture, poikilitic texture, forked texture, emulsion solid separation texture, skeletal texture, etching texture and porphyroblastic texture. The main structure types are breciated structure ?disseminated structure?banded structure and vein structure. Country rock aiteration type in mining area are mainly biotitization, carbonatation, albitization, silicification, chloritization and carbonatation.Lala deposit mineralization can be divided into four metallogenic periods: volcano sedimentary original source bed formative period, regional metamorphism metallogenic period, hydrothermal mineralization period and supergene oxidation period. Then regional metamorphism metallogenic period and hydrothermal mineralization period are subdivided into four stages: magnetite-apatite stage, metal sulfide stage, chalcopyrite-pyrite stage and hydrotherm stage. The first stage mainly occured magnetite formation,and typical mineral assemblage is magnetite+apatite(potassium feldspar) combination. The second stage mainly formed magnetite and other major metal minerals, with typical mineral assemblage +magnetite+chalcopyrite+pyrite combination; The third stage mainly produce fchalcopyrite, pyrite and some gangue minerals, and typical mineral assemblage is chalcopyrite+pyrite+quartz+calcite+biotite. Phase 4 mainly produce gangue minerals accompanied by a few chalcopyrite and pyrite. The last supergene oxidation period mainly develop limonite,hematite,malachite, azurite,calcite,etc.In this paper, the process of mineralization of the Lala copper deposit is roughly as follows: In the latest Paleoproterozoic(about 1700Ma) early of cracking Panxi rift,with strong undersea volcanic activity, study area formed undersea volcano-sedimentary rocks of Hekou Group, the original copper enriched layer(source bed) and initial gathering of ore- forming elements in Hekou Group, such as PEG, LREE, Cu, Au. After the experience of hydrothermal mineralization in ancient(about 1200 Ma-1000Ma), because of the Yangtze plate and Huaxia plate collage, rocks of Hekou Group and original source bed of copper and iron has experienced many periods of regional dynamic-thermal metamorphic transformation happened diagenesis and mineralization, the metal elements such as copper, gold, iron and molybdenum in the original source bed was further activation and migration, prompted them to further concentration that formed initially copper and iron ore, which are rich and thick, as seen in Luodang mining area. Finally during Neoproterozoic( 1000- 850Ma) hydrothermal reformation period,under the influence of extensive metamorphism metamorphism,with the ultrabasic rock Jinning period(Pyroxenite, gabbro) intrude into Hekou Group, led metallogenic material which in the Lala copper(gold) deposit final migration and enrichment and mineralized in the Hekou Group's most advantageous parts(high porosity and high permeability rocks), formed many rich copper and iron ore more have mesh-vein structure which in shear joint that is overlaying formed in previous two period schistosity and late schistosity that is perpendicular to early-formed schistosity.Above all, Lala copper(gold) deposit and typical iron oxide copper gold deposits(IOCG) characteristics have a certain similarity in features, but whether to belong to IOCG, is worth further researching. |
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