| 摘要 | 扬子地块西南缘是中国甚至世界上独特的、大面积分布的低温热液矿床矿集区,广泛发育Au、Ag、Hg、Sb、As、U、Cu、Pb-Zn以及重晶石、萤石、冰洲石等低温热液矿床,其中不少矿床属大型-超大型矿床规模.以沉积岩为容矿岩石的卡林型金矿(又称微细浸染型金矿),则是该区重要的矿产类型.目前已发现烂泥沟、紫木凼、戈塘、金牙、高龙等大、中型卡林型金矿床6个,小型矿床、矿点(矿化点)近200余处.主要集中分布在黔西南、滇东南和桂西北的交界地区,周边被深(大)断裂带所限,大体呈三角形,俗称"金三角".首先对该区众多的基性-超基性岩浆岩的同位素年代学及其反映的地质背景进行了较系统的研究,选择革挡和八渡(D)、纳哥(P)、烂泥沟和丫他(T)等代表性金矿床,进行了系统的流体包裹体岩相学、显微测温学、单个包裹体的激光Raman、流体包裹体群中的微量元素以及Rb-Sr、He-Ar、同位素组成等研究,获得了大量数据,并拍摄了大量包裹体照片(约400张).该次对该区卡林型金矿成矿流体地球化学的研究,作者认为在以下方面取得一定进展:(1)发现(或证实)了该区卡林型金矿富含C0<,2>相包裹体,并且种类众多,提出了卡林型金矿的成矿作用,经历了流体不混溶的过程(沸腾作用):(2)进一步证实了有机质参与卡林型金矿的成矿过程:(3)证实了盆地超压流体的存在,并提出了卡林型金矿的大规模成矿作用是"盆地超压流体-矿源岩-盆地伸展"耦合的观点. |
| 其他摘要 | The southwestern Yangtze craton is an unique large epithermal mineralization area in China or even in the world. There are various epithermal mineralization of Au, Ag, Hg, Sb, As, U, Cu, Pb-Zn, barite, fluorite and Iceland spar with some deposits in large scale. The Carlin-type gold deposits (or disseminated gold deposits) is an important type of deposits in the area. Six large gold deposits of Lannigou, Zimudang, Getang, Jinya, Gaolong, Yata and about 200 small gold deposits in the area have been documented. These gold deposits are mainly distributed in the conjunction of Yunnan, Guizhou and Guangxi provinces. Since the discovery of the first Carlin-type gold deposit in 1978 in China, a large amount of investigations on geological background, ore component, wallrock alteration, occurrence of gold etc. have been carried out and lots of research have been achieved. However, the fluid inclusion study of the Carlin-type gold deposits in the area only has been carried in some of deposits individually. The gold mineralization occurred in various strata from Cambrian to Cretaceous system in age and controlled by various kinds of structures which include Devonian unconformity plane (D), Permian palaeo-erosion plane (P) and high angle faults in Triassic strata (T). What are the difference and relationship among the ore-forming fluids of gold deposits formed in strata in various ages? When those basic-ultrabasic magmatic rocks in the area were formed and what is the relationship between their intrusion and the large scale Carlin-type gold mineralization? On the basis of previous research, the author has systematically undertaken the isotopic geochfonologicat study and the geological background of those basic-ultrabasic magmatic rocks, and also has systematically carried out fluid inclusion studies including fluid inclusion phase assemblages, microthermometry, Laser-Raman spectrorhetry of single inclusion, trace elements and Rb-Sr, He-Ar isotopic analysis of the fluid inclusions. Through the above work, a large amount of data was gained and about 400 photos of fluid inclusions were taken, and the major achievements are obtained as following: 1. The lithosphere underneath the Carlin-type gold mineralization area had been involved many times of extension and deformation, at least from Hercynian to Late Yanshannian, in form; of multi-stage intrusions and eruptions of basic-ultrabasic magmatic rocks which formed the material base for the formation of the Carlin-type gold deposits in large scale in the area. In particular, the intrusion of the Late Yanshannian (102-85 Ma) ultrabasic rocks might indicate the re-extensional event of the lithosphere or the re-activation of the deep crustal fractures and are believed to trigger the Carlin-type gold mineralization in large scale. The Carlin-type gold deposits occurred in strata of various age in the area have many features in common among them in terms of geological feature, component, wallrock alteration, and the occurrence of gold, and have similar features comparing with those of the Carlin-type gold deposits in USA. However, it is discovered that there are abnormal platinum-group elements concentrations in ores and the fluids. The typical phase assembladges of the fluid inclusions show that there is no obvious difference in types among fluid inclusions from various Carlin-type gold mineralization hosted in strata of various ages (D, P, T). There are mainly NaCl-H2O type of inclusions with V+L p:hases and CO2- rich type of inclusions with LC02, LC02+L, VC02+L, VCO2+LCO2+L, or VCO2 phases respectively.. The CO2-rich inclusions and normal NaCl+H2O inclusions are commonly observed in same samples with the same homogenization temperature (Th). This indicates that the immiscibjlity (boiling) process of the hydrothermal fluid was involved in gold mineralization of the Garlin-type gold deposits in the area. A large amount of microthermometric data of fluid inclusions indicates that the homogenization temperatures and trapping pressures of fluid inclusions in quartz veins from deposits hosted in strata of various ages are slightly varied. The homogenization-temperatures and trapping pressures of fluid inclusions in quartz veins from the Lannigou and the Yata gold deposits, as the representatives of the gold deposits hosted in Triassic sediments, are mainly varied from 200 to 220 °C and from 1180 to 1500 bars respectively. However, those of fluid inclusions in quartz veins from the Gedang and the Badu gold deposits, as the representatives of the gold deposits hosted in Devonian sediments, are mainly varied from 230 to 240 ℃ and from 1180 to 2000 bars respectively. The salinity of the inclusion fluids in quartz veins from various deposits is mainly varied in the range from 3.5 to 6.5 wt% NaCl. A large amount of Laser-Raman analysis for individual inclusions indicate that the C02-fich inclusions contain 75～98.5 mole% of CO2, 2.7-17 mole% of N2 and 2.3-8 mole%: of ,CH4 respectively. In addition, the Laser-Raman analysis for individual inclusions show that there are some nearly liner correlation between the C and N contents in various types of inclusions. The ratio of the C/N (C and N contents) of the CO2-rich inclusions with only liquid CO2 observed is about 2:1, whereas that of the CO2-rich inclusions with liquid CO2 and liquid NaCl+H2O phases observed is about 8:1. This implies that the organic matter had involved in the mineralization process of the Carlin-type gold deposits in the area. The trace elements study of the inclusions fluids from various gold deposits in the area shows that the inclusion fluids from minerals formed in various hydrothermal stages contain nof only high contents of Co, Ni, Cu, Pb, Zn, but also relatively high content of Pt. It is believed that they might be sourced from basic volcanic matters or from the black rocks in the basement. 8. The Rb-Sr and He-Ar isotopic studies of the inclusion fluids show that the Carlin-type gold mineralization occurred in the Late Yanshannian period (around 85 Ma) and the ore-forming fluids are mainly sourced from the meteoric water or the basin fluids related to the meteoric water. The field geological investigation and the fluid inclusion study indicate that the over-pressure basin fluids were existed and were associated with the large scale Carlin-type gold mineralization in the area. It is believed that the gold precipitation form the ore-forming fluids might be trigged; by the reduction of the organic matters. In general, through the hydrothermal fluid geochemical study of the Carlin-type gold deposits in the area, the author believes that some progresses have been achieved. (1) Various types of CO2-rich inclusions have been discovered and the immiscibility (boiling) process of the hydrothermal fluids was believed to have been involved in the Carlin-type gold mineralization in the area; (2) It is further proved that the organic matters involved the process of the mineralization; (3) the over-pressure basin fluids is proved to have been existed and played important role in the large scale Carlin-type gold mineralization. |
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