内蒙古八大关斑岩型铜钼矿成矿作用研究

发布时间：2018-06-06 09:37

本文选题：成矿作用 + 流体包裹体　；参考：《中国地质科学院》2015年硕士论文

【摘要】：八大关斑岩Cu-Mo矿床是我国内蒙大兴安岭成矿带北段典型的斑岩型Cu-Mo矿床之一,地处中亚造山带东段,额尔古纳地块内嵯岗-得尔布尔隆起区。矿体主要产出在印支期花岗闪长斑岩体内和岩体的接触带,主体呈脉状展布。矿床具有典型的斑岩型铜矿蚀变分带现象,从岩体中心向外依次发育钾化带→石英-绢云母化带→绢云母花带→青磐岩化带,蚀变与矿化关系密切。矿化以铜钼矿化为主,辉钼矿主要伴随石英脉产出,以脉状分布为主,主要分布在石英-绢云母化带；黄铜矿主要呈浸染状、细脉浸染状分布,与绢云母化带关系密切,少数分布在石英-绢云母花带。本文对矿区主要侵入岩的岩相学、成岩成矿时代和成矿流体特征进行了查明,较以往工作进行了更加系统的研究。镜下鉴定结果显示矿区侵入岩岩性主要有黑云母花岗岩、花岗岩、钾长花岗岩、花岗斑岩、花岗闪长斑岩等；LA-MS-ICP-MS锆石U-Pb定年结果显示,矿区主要侵入岩集中分布在(243～237Ma)和(231～229Ma)两个阶段,均与印支期构造-岩浆活动密切相关。此外,获得辉钼矿Re-Os等时线年龄为228.7±3.1Ma,与成矿花岗闪长斑岩的就位年龄(230.5Ma)在误差范围内基本一致,说明八大关成矿事件发生在中三叠世,与印支晚期构造-岩浆活动有关。矿区侵入岩地球化学研究表明,矿区印支期侵入岩总体上表现为高SiO2和富A1203,低MgO和TFe2O3,富集LREE、LILE和亏损HREE、HFSE,弱的Eu负异常,显示具有俯冲环境岛弧花岗岩的特征。结合矿区侵入岩锆石的Hf同位素研究,表明矿区印支期侵入岩的初始岩浆起源于新元古代早期由亏损地幔派生的新生年轻地壳的部分熔融,在MASH区加入了少量的古老地壳的。流体包裹体研究表明,八大关铜钼矿床流体包裹体类型丰富,有V型富气相包裹体、L型富液相包裹体、S型含子矿物多相包裹体,C型含CO2的三相包裹体。成矿流体演化过程具有早、中、晚三阶段的特点,其均一温度主要集中在238℃～572℃,盐度集中在0.42～63.13%NaCleqv,反映了岩浆热液的特点。铜钼金属元素的沉淀主要发生在中阶段,但其沉淀机制却发生了解耦,辉钼矿的大量沉淀主要与减压沸腾作用有关,黄铜矿的沉淀主要与温度降低有关。岩相学研究和激光拉曼分析表明,成矿流体早中阶段流体包裹体除H2O外,还含CO2和少量N2；子晶可见石盐、硬石膏、赤铁矿和硫化物；晚阶段石英脉包裹体只含H2O,无CO2和子晶。成矿流体由早中阶段的H20-NaCl-CO2体系逐渐向晚阶段的H2O-NaCl体系演化。H-O-S同位素分析结果均表明,成矿流体主要来源于岩浆热液,大气水的混合比例有限；成矿物质主要来自地幔,并有少量围岩中S的参与。在印支期,研究区主要处于鄂霍茨克洋朝南向中蒙联合板块俯冲、碰撞的构造背景。结合侵入岩的地球化学特征和Hf同位素分析结果,本文认为八大关铜钼矿床形成于印支晚期鄂霍茨克洋俯冲向陆陆碰撞转换的构造环境,而区域规模的动力变形变质作用暗示蒙古鄂霍茨克洋在额尔古纳地区的的闭合时间可能在印支晚期。
[Abstract]:The Ba Da Guan porphyry Cu-Mo deposit is one of the typical porphyry type Cu-Mo deposits in the northern part of the Greater Khingan Range metallogenic belt in Inner Mongolia. It is located in the eastern part of the Central Asian orogenic belt and in the Eergu'Na block. The ore body is mainly produced in the contact zone of the granodiorite porphyry and rock mass in the Indosinian period, and the main body is in the vein. The deposit is typical of the deposit. The alteration zoning phenomenon of porphyry copper deposits has developed from the center of the rock mass to the potash zone, quartz sericite belt, sericite flower belt and green pan rock zone. The alteration and mineralization are closely related to mineralization. The mineralization is mainly copper molybdenum mineralization. The molybdenite is mainly accompanied by quartz veins, mainly in the vein distribution, mainly in the quartz sericite zone; Copper deposits are mainly disseminated, veined disseminated and closely related to sericite zones, and a few are distributed in quartz sericite belts.
In this paper, the petrography of the main intrusive rocks, the age of diagenesis and mineralization and the characteristics of the ore-forming fluid have been identified, and more systematic studies have been carried out than previous work. The results of microscopic identification show that the lithology of the intrusive rocks in the mining area mainly include the black mica granite, granite, potassium feldspar, granite porphyry, granite diorite porphyry, and so on, and LA-MS-ICP-MS zircon U The -Pb dating results show that the main intrusive rocks in the mining area are concentrated in (243 to 237Ma) and (231 to 229Ma), which are closely related to the Indosinian tectonic magmatism. In addition, the Re-Os isochronous age of the molybdenite is 228.7 + 3.1Ma, which is basically the same as that of the ore-forming granodiorite in the range of error (230.5Ma). The Guan Cheng mine occurred in the middle three Permian, which is related to the tectono magmatic activity in the late Indo China.
The geochemical study of intrusive rocks in the mining area shows that the Indosinian intrusive rocks in the mining area were generally high SiO2 and rich A1203, low MgO and TFe2O3, enriched LREE, LILE and defective HREE, HFSE, and weak Eu negative anomalies, showing the characteristics of the subducted island arc granite. The Hf isotopes of zircon from the intrusive rocks in the mining area indicate that the Indosinian intrusive rocks in the mining area were shown. The initial magma originated from partial melting of new young crust derived from depleted mantle in the early Neoproterozoic, and a small amount of ancient crust was added to the MASH area.
Fluid inclusion studies show that the fluid inclusions in the Ba Da Guan copper molybdenum deposit are rich in fluid inclusions, including V rich gas inclusions, L rich liquid inclusions, S type mineral inclusions and C type CO2 containing three phase inclusions. The evolution process of the ore-forming fluid has the characteristics of early, middle and late three stages, and the homogenization temperature is mainly concentrated at 238 to 572 degrees C, and salinity is mainly concentrated. The concentration of 0.42 ~ 63.13%NaCleqv reflects the characteristics of magmatic hydrothermal solution. The precipitation of copper and molybdenum metal elements occurs mainly in the middle stage, but the precipitation mechanism has been decoupled. The precipitation of molybdenite is mainly related to the effect of decompression and boiling, and the precipitation of chalcopyrite is mainly related to the temperature reduction.
Petrographic study and laser Raman analysis show that the fluid inclusions in the early and middle stage of the ore-forming fluid contain CO2 and a small amount of N2 except for H2O, and the subcrystals can be seen as stone salt, anhydrite, hematite and sulfide, and the late phase quartz vein inclusions only contain H2O, without CO2 and subcrystal. The metallogenic fluid is gradually from the H20-NaCl-CO2 system of the early middle stage to the H2O-NaCl in the late stage. The results of.H-O-S isotope analysis show that the ore-forming fluids are mainly derived from magmatic hydrothermal fluid, and the mixing ratio of atmospheric water is limited; the metallogenic material mainly comes from the mantle and has the participation of S in a small number of surrounding rocks.
During the Indosinian period, the study area was mainly in the subduction of the Sino Mongolia joint plate in the south of Okhotsk ocean and the tectonic setting of the collision. Combined with the geochemical characteristics of the intrusive rocks and the results of Hf isotope analysis, this paper holds that the Ba Da Guan copper molybdenum deposit formed in the tectonic setting of the transition from the subduction of the late Indo to the Okhotsk ocean to the continental collision, and the regional scale. Dynamic deformation and metamorphism suggest that the closure time of Mongolia Okhotsk ocean in Eergu'Na area may be in the late Indosinian period.
【学位授予单位】：中国地质科学院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.41;P618.65

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