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Stable Isotope Geochemistry Research of LaLa Iron Oxide-Cu-Au-U (IOCG)Deposit

Author: WangZuo
Tutor: LiZeQin
School: Chengdu University of Technology
Course: Geochemistry
Keywords: LaLa IOCG deposit Stable isotope Ore-forming fluid
CLC: P597
Type: Master's thesis
Year: 2013
Downloads: 36
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Abstract


IOCG deposit is a type of unique hydrothermal iron oxide copper-polymetallic deposit in terms of output environment, geological characteristics, and its metallogenic mdchanism. Because of its great economic value, since1992IOCG was raised by the Hitzman attracted huge international academic response and attention, has become the second new research upsurge after porphyry copper, VMS-type and SEDEX-type deposit,and epithermal gold deposit,ore and mineral exploration in the field of research and a new climax. However, the domestic research on IOCG deposits in its infancy, the need to constantly research knowledge and accumulated experience.LaLa deposit in Huili of Sichuan is located on the western margin Yangtze middle of Kangdian axis, which is the largest copper deposit in north-south sides copper polymetallic metallogenic belt of western margin of the Yangtze Sichuan and Yunnan, is also China’s major copper producer base. Predecessors did a lot of research on Lala deposit, but about its genesis has been divided, and until recent years some scholars re-determine the Lala as iron oxide copper-gold (IOCG) deposits.This paper studies Lara deposit as IOCG from his stable isotope geochemistry, and discusses the main source of ore-forming fluids, mainly achieved the following knowledge and progresses:(1) Lala IOCG metallogenic geological characteristics:it occurs in the Paleoproterozoic Taipa estuary community group, as a volcano-sedimentary metamorphic rocks, host rocks are mainly schists and albite rock types; Lala deposit in addition to Fe, Cu mineralization, but also enriches Au, Ag, Mo, REE, Co, P and other elements, the main ore minerals are magnetite, chalcopyrite, pyrite, molybdenite, apatite, whose iron oxide content is much larger than the iron sulfide content. The mainly form of Metallic mineral assemblage is magnetite-chalcopyrite-pyrite. Ore structures are mainly stripes-banded, veined-stockwork and disseminated structures, ore textures are mainly euhedral, subhedral, non-shaped grains institutions. Regional and peripheral developmental scale albitization grows very well both in the region and periphery.Combined with regional tectonic evolution that Lala copper mineralization is divided into regional metamorphism and hydrothermal mineralization stage of mineralization, which can be divided into four phases:magnetite-apatite phase, magnetite-metal sulfide phase, sulfide phase, the late stages of poor veins.(2)LaLa IOCG deposits regional metamorphism metallogenic phase of the Ⅰ stage ore-forming temperature in430-490℃, the best temperature in460℃, stage Ⅱ ore-forming temperature at350-450℃. Hydrothermal ore-forming stage Ⅲ ore-forming temperature determine between250-350, and the best mineralization temperature320℃; Stage IV metallogenic temperature is110-200℃.(3)δ34S values of mineral are concentrated between0‰~3‰, value of total sulfur in mineralization solution δ34SΣS=1.68‰-2.82‰. Through comparison on sulfur isotopic composition with similar deposits illustrates the source of sulfur in Lala copper mineralization is mainly from mantle.(4) Whole-rock and sulfide Pb isotopic composition of radiogenic Pb content is extremely high with wide variation range, suggesting that the source of lead with mixed characteristics. The study on hole rock Pb isotopic and lead isotope mixing isochrone mode analysis determines the source of Pb in Lara deposit from upper crust and upper mantle and lower crustal contamination environments.(4) H-O isotope studies show that regional metamorphic ore forming fluids is mainly metamorphic water,however,in the hydrothermal mineralization stage, the ore-forming fluid transformed to magmatic hygrothermal from meteoric water.(5) The average valueδ13C of calcite is-2.45‰, closed to the mantle-derived carbon range. The value ofδ13C of Ore-forming fluids ranges from-4.05‰to-0.8‰, and the average of δ18O is5.33‰, combined with metallogenic geological characteristics,indicating that the main sources of carbon is from late Paleoproterozoic, igneous for the sake of volcanic eruptions with the nature of mantle-magmatite mixed basic rocks and influences by meteoric-formed carbon.(6) The above analysises show the deposit is formed through the following process:In late Paleoproterozoic2000-1680Ma, western margin of the Yangtze basin was in continental rift environment, originated in the upper mantle magma eruption, and mixed with upper crustal material during the process forming Sanhe group alkaline volcanic. Sulfur isotope, carbon isotope, lead isotope also indicated nature of the magma-mantle source, illustrating the volcanic eruption carried out a large number of ore-forming materials into an initial source bed. In Mesoproterozoic about1000Ma ago, accompanied by a collage of Rodinia supercontinent role, the basement rocks in western margin of the Yangtze Kangdian axis developed metamorphism, namely Jinning movement. The value of δ18O and8D in ore fluids proved this period is mainly metamorphic fluids. In the early metamorphism, mainly developed magnetite, with the weakening of metamorphism, REE ore and Fe, Cu, Mo, Au, Co of pay-rock began to move to ore-forming fluids partly and enriched in benefit setting. Metamorphism leaded schistose rocks and minerals to foliated, metallogenic material formed lamellar structure ore along schistosity. About850Ma ago, because of Rodinia supercontinent cleavage event, plume-origined gabbro intruded into Hekou Group, provided thermal driving force for forming fluid leadind the further enrichment of ore-forming elements. The value of δ18O,AD,δ13C indicated magmatic hydrothermal ore-forming fluid evolved from magma hydrotherm to meteoric water during hydrothermal mineralization period. In the early days, magma was the dominant factor, with formation of stockwork structure displayed the shear joints of late schistosity superimposed on top of the earlier foliation, and late foliation direction was perpendicular to the early schistosity. As the strengthening of the role of meteoric water, advanced late oxidation ore-bearinf hydrothermal making some early chalcopyrite, pyrite recrystallized into single coarse particles, with higher degree of self-shaped in the form of calcite-sulfide veins.

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CLC: > Astronomy,Earth Sciences > Geology > Geochemistry > Isotope geology and geochronology
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