西藏哈海岗钨钼多金属矿床地球化学特征及成因启示

发布时间：2018-05-17 05:35

  本文选题：成矿期次 + 成矿岩体　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：哈海岗矽卡岩型W-Mo多金属矿床位于西藏念青唐古拉成矿带东段中部,冈底斯弧背断隆带南缘,受达龙区域断裂带控制。目前研究程度较低,仅限于矿床地质与成矿、成岩年龄的研究,本文主要针对矿床地质特征、成矿岩体厘定及其地球化学特征和成矿物质来源的示踪展开研究,有助于进一步和冈底斯成矿带其他矿床对比,探讨成岩-成矿机制,总结区域成矿规律。结合野外地质调查和显微镜下观察,将哈海岗矽卡岩型成矿作用划分为矽卡岩期和石英-硫化物期,包括干矽卡岩阶段、湿矽卡岩阶段、石英-辉钼矿阶段和石英-铁铜铅锌硫化物阶段。前人对矿区出露花岗闪长岩(56.1Ma)和二长花岗岩(57.02-58.66Ma)定年显示晚于辉钼矿成矿年龄(63.2Ma),而笔者通过野外采样发现花岗闪长岩发育浸染状白钨矿和辉钼矿化,二长花岗岩发育石英-辉钼矿脉。因已有岩体年龄无法解释该矿化现象,笔者对矿化岩体重新定年,发现花岗闪长岩发育侏罗纪和古新世两期,锆石U-Pb年龄分别为194.5±1.8Ma和63.82±0.7Ma,二长花岗岩年龄为64.63±0.8Ma。根据矿化现象、成岩年龄与矿床分带特征,认为成矿岩体很可能为古新世花岗闪长岩或二长花岗岩。古新世花岗闪长岩和二长花岗岩成岩年龄基本一致,均具有高的SiO2含量(69%-76%)、全碱含量(K2O+Na2O=6.5%-9.3%)和FeO*/MgO比值(3.3-7.7),表明它们经历了高程度结晶分异,且二长花岗岩结晶分异程度高于花岗闪长岩。通过主微量元素分析发现,哈海岗古新世花岗闪长岩和二长花岗岩具有高分异I型花岗岩特征。通过哈海岗金属硫化物和矿区岩体及旁那组沉积围岩S-Pb同位素测试,发现其金属硫化物δ34SCDT集中于2.7‰-5.4‰,平均值为4.08‰;研究认为硫很可能来源于成矿岩体岩浆,且成矿热液受到了围岩地层的混染作用。铅同位素比值相对稳定,极差均小于0.1‰;构造环境演化图解中,金属硫化物铅同位素点落在上地壳演化线上,且集中均匀分布,指示矿物铅主要来自于上地壳。综合分析认为,哈海岗成矿物质主要来源于壳幔混源的成矿岩浆。
[Abstract]:The Hahaigang skarn type W-Mo polymetallic deposit is located in the middle of the eastern section of the Nianqingtang Gula metallogenic belt in Tibet and is controlled by the Dalong regional fault belt. The present study is limited to the study of ore deposit geology, mineralization and diagenetic age. This paper mainly focuses on the geological characteristics of the deposit, the determination of ore-forming rock mass, the geochemical characteristics and the trace of the source of the ore-forming material. It is helpful to further compare with other deposits in Gangdis metallogenic belt, discuss the diagenesis-metallogenic mechanism and summarize the regional metallogenic regularity. Based on the field geological survey and microscopic observation, the mineralization of the hahaigang skarn type is divided into skarn stage and quartz-sulfide stage, including dry skarn stage and wet skarn stage. Quartz-molybdenum stage and quartz-iron-copper-lead-zinc sulfide stage. The dating of protruding granodiorite (56.1 Maa) and monzomorphic granite (57.02-58.66 Ma) shows that the age of mineralization is 63.2 Mag later than that of molybdenum ore. However, the authors found that granodiorite developed disseminated scheelite and molybdenum mineralization through field sampling. The monzogranite developed quartz-molybdenum vein. Because the age of the existing rock mass can not explain the mineralization phenomenon, the author has redated the mineralized rock body and found that the U-Pb age of zircon is 194.5 卤1.8Ma and 63.82 卤0.7 Ma. the age of monzogranite is 64.63 卤0.8 Ma. during the Jurassic and Paleocene stages of granodiorite. According to the mineralization phenomenon, diagenetic age and zonation characteristics of the deposit, it is considered that the ore-forming body is probably Paleocene granodiorite or monzomorphic granodiorite. Paleocene granodiorite and monzomorphic granodiorite have the same diagenetic age, both have high SiO2 content (69-76) and total alkali content (K _ 2O Na _ 2O _ 2O _ (6.5) -9.3%) and FeO*/MgO ratio (3.3-7.7), indicating that they have experienced high degree of crystallization differentiation. The degree of crystal differentiation of monzogranite is higher than that of granodiorite. Through the analysis of main trace elements, it is found that the hahaigang granodiorite and the monzomorphic granodiorite have the characteristics of high differentiation I type granite. Based on the S-Pb isotopic measurements of the Hahaigang metallic sulphide and the orebody and its surrounding rocks, it is found that the metal sulphide 未 34SCDT is concentrated in the range of 2.7 鈥，

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