| Qilian Orogen Belt has been researched by many geologists for a long time,which locates at the north of Tibet and is famous as one of proliferative orogenic. Lotsof researches about North-Qilian has been carried out, but researches about acidintrusive rocks in Mid-Qilian are less than North-Qilian. This paper introduceslitho-geochemical characteristics of Yinshenggou magmatic rocks, preliminarilyinvestigates metallogenic significance of magmatic rock combining with theShangjiake skarn pyrite deposit that is related with Yinshenggou Magmatic rock.According to the results of geological survey, Yinshenggou magmatic rockdistributes like a spindle on the whole, its long axis strike E-W, with the length of25km, width of12km, this area of which on the earth surface is about327km2. Fromnorth to south, magmatic rocks appears evolution sequence which changes fromneuter to acidity gradually. Diorite dominates the northern part of YinshenggouMagmatic rock; biotite granite, porphyritic biotite granite and fine-grained granitedistribute in the southern part of Yinshenggou Magmatic rocks. The main stratumsfrom old to new consisted of Paleoproterozoic Huangyuan Group, Liujiatai Group(Pt1l), Dongchagou Group (Pt1d), Mesoproterozoic Jixianian Huangzhong Group andMoshigou Group (Jxm), Qingshipo Group, Kesuer Group (Jxk). More than20orepoints has been discovered, most of which locate at the place where magmatic rockscontacted with carbonate rocks.SiO2-(Na2O+K2O), ACNK-ANK, AR-SiO2and SiO2-K2O graphics are used inthis paper to analysis major element characteristics, trace elements and REE elementsare analyzed in the ORG graphic and Chondrite normalized distribution graphic; traceelements method and differentiation index are used to research differentiation andevolution degree; major element method and trace element method are use to researchtectonic environment.Petrology and geochemistry suggests that Yinshenggou magmatic rocks is richedin Si (63.24%~73.25%), K2O (1.14%~6.93%), Na2O (1.72%~5.92%), but barren in Ca (0.63%~4.08%), and is classified as calc-alkaline series, with the characteristic ofS-type granites. The contents of trace elements Ba, Th and Sr change widely, large ionlithophile element Rb is enriched relatively, but K is dificited; high field strengthelements Th, Ta, Nb, Hf, Zr change in a wide range, Y is enriched relatively, but Yb isdificited. REE characteristics could be divided into three categories:(1) the fist groupis of high REE contents, LREE is richer than HREE whose trend is flat, δEu is low;(2)the second group is of lower REE contents, the fractionation is low, the formation ofdistribution is flat, δEu is not obvious;(3) the third group is of low REE contents,LREE changes in a wide range, HREE changes in a focused range, δEu is strong.Above all, this rock formed in the abatement plate margin environment whichappeared before collision mitigation. The magma in this area which formedYinshenggou magmatic rocks were mixed with crust material and mantle material.The stratums at Shangjiake deposit dominated by lower group of Dongchagougroup, Tertiary and Quaternary. The mine was located at the middle part betweenQianshagou anticline and Daxia rewind syncline, which is proved to be a monoclinicstructure, and slopes eastly. The magmatic rocks at the mine area are edge phase ofYinshenggou Magmatic rock, the main lithology is diorite.The ore bodies are mainly hosted in the strata of Lower Sinian Dongchagou Fm.of Upper Neoproterozoic, and are separated into two belt by diorite: belt1locates atthe upper, and belt2is at the lower. Belt1is of large-scale, the main ore bodies ofwhich are11,14,16and17; the main ore bodies of belt2are21and22. Ore typescontain dense lump ore, dense disseminated-lumpish ore, disseminated-irregularveinlet ore, sparsely disseminated-small lumps ore. The ore structure types containedmassive structure, disseminated structure, banded structure, brecciated structure, veinstructure, earthy structure and colloidal structure. The ore texture types mainlyincluded hypidiomorphic-changed granular texture, dissolution texture, residualtexture and crush texture. The main elements of the ore are S and Fe. The mainbeneficial element is Ta; harmful elements contain F, As, Pb, Zn; some other commonelement is P which is kept in the form of P2O5.There are mainly four wall rock alteration: skarnization, chlorite, silicificationand secondary change. The mineralization period can be divided into four phases:skarn phase, epidote-chlorite-sulfide phase, quartz-sulfide phase, quartz withoutmineral phase.The conclusions are made based on the preliminary research results aboutrelationships between Shangjiake pyrite deposit and diorite, this paper suggest that:(1) diorite not only offered mineral elements to ore bodies, but also carried the mineralmaterials from deeper stratums;(2) magma with high temperature adsorbed andheated the stratums leading to thermal contact metamorphism, and drove and recycledthe underground water with the force of regional tectonic pressure, and ores areformed at suitable areas;(3) diorite not only controlled the horizon of the beltsspatially, but also worked as inter-layer which was conductive to sediment ore-bearingfluids. |
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