Geothermal Events And Its Metallogenic Significance Of Carlin Type Gold Deposits In Youjiang Basin

This article applies the theory of regional metallogeny,deposit organic geochemistry,basin sediment-tectonic evolution and mineralization,deposit geology geochemistry and geotectonic marginal mineralization etc to the systematic study of Youjiang basin sediment-tectonic evolution history and its associated geological thermal events,then investgating the geological thermal events type,characteristics and the formation mechanism, analyzing the organics in deposits which have the tracer significance in the geological thermal events and play an important role in gold mineralization,discussing the relationship between Carlin-type gold deposits in northwestern Guangxi mineralization and the organics and the geological thermal events as well as the minerogenetic mechanism of gold, summarizing the time-space distribution feature and the metallogenic regularity of Carlin-type gold deposits in northwestern Guangxi metallogenic province,Finally evaluating the ore-finding prospects based on the comprehensive research.The main cognitive and research results are as follows:1.With heat source as the main line and geological thermal events as the key factors, we research the Youjiang basin’s sedimentary-tectonic evolution process and the associated geological thermal event, mineralization, ore-controlling significance systematically.In the process of Youjiang basin’s sedimental-tectonic evolution,the main geological thermal events related with the mineralization of Carlin-type gold deposits are deep buried sedimentary stratas’geothermal gradient,geotectonic position and tectonic movement,magma-volcanic activity as well as hydrothermal activity.Among them, the deep buried sedimentary stratas’geothermal gradient is the most important and direct thermal event, for the metallogenic materials preliminary enrichment,second distribution,remobilization,reconstruction,It play a different meaning of direct and indirect effect, as "the geological thermal events of mineralization".2.This paper comprehensive evaluated the deep buried constructive role and geological thermal events of sedimentary statum in the Youjiang basin.The evolution of Youjiang basin had experienced Passive continental margin rift basin stage of Devonian-Early Permian, back-arc basin stage of Late Permian-early Triassic, extrusion and downwarping basin stage of In Triassic-late Triassic, after the late Triassic intracontinental extrusion fold uplift into land. The maximum thickness of sedimentation belonging to Youjiang basin can be nearly meters (or The lower and middle Triassic formation of maximum thickness can be CTKM meters). According to the geothermal gradient for3～5°C/100m to calculate, the Youjiang basin bottom temperature can be up to300～500°C (or Trias formation at the bottom of the ground temperature can reach300～500°C). Therefore, the Metallogenic geologic time belonging to Carlin-type gold deposits in the region of the northwest of Guangxi, the Youjiang basin formation deep buried geothermal temperature can completely satisfy the Carlin-type gold deposits mineralization needs.3.This paper discusses the Youjiang basin in northwest of Guangxi sedimentation-structure in the evolution process of the nature of the magma-volcanic activity and the geological thermal event metallogenic ore-controlling significance.The mineralization of this Carlin-type gold deposits mainly occurs in the late indosinian period and early yanshanian, the magma-volcanic activity produced by the geological thermal events, its metallogenic meaning mainly manifested in two aspects:(1)the formation of source bed.(2) providing heat and thermal fluid.4.Have been Comprehensive analysised the characteristic of the hydrothermal activity in Youjiang basin and the geological hot events significance.According to the northwest Guangxi Carlin-type gold deposit geological、geochemical comprehensive researched result, and we know that the formation process of the northwest Guangxi Carlin-type gold deposit, ore-forming fluid is mainly basin thermal brine. Mineral fluid inclusions and the largest coal vitrinite reflectance results indicate that the northwest Guangxi Carlin-type gold deposit’s metallogenic temperature range mainly distributed in100～350°C,which shows the existence of geological thermal events.5.Using of the latest theory that mineral deposits and geochemistry of mineral deposits,on the basis of previous studies, conducting comprehensive conclude, and considering the gold deposits of Northwest Guangxi is a kind of Carlin-type gold deposit that relates to mineralize of basin thermal brine.6.Having been explored the organic matter of the Youjiang Basin Carlin-type gold deposits and its geological thermal events tracer and metallogenic significance. The organic matter of the Youjiang Basin Carlin-type gold deposits contain native-kerogen and migrating organic fluid, and organic carbon content is0.18%-2.95%,an average of0.97%.Primary organic matter include II-kerogen and little I-kerogen. Causing the organic matter of Youjiang-basin occur mature anomaly geological thermal events was mainly the deep burial diagenesis of sedimentary formation that caused geothermal heating, but with the effect of the geological thermal events which include magmatic intrusion,volcanic eruption,tectonic compression,metamorphic damage,radioactive disintegration and so on was obviously different.7.Have been studied the metallogenic significance of organic matter and its thermal mature product. The biomarker research results show that it has infiltration of precipitation and Bacterial microorganisms participated in the process of mineralization, and it has organic fluid from migration participated. This indicates that the mineralization mechanism of gold contained the mixing effect of different physical and chemical properties of the fluid. The mineralization reaction when the temperature was not high that it generally no higher than100℃; Metallogenic depth was not deep, and its depth was not more than2000m.8. The hydrogen-oxygen isotope geochemistry study has confirmed that the evolution of Youjiang basin and atmospheric precipitation as its main characteristics of the water. Hydrogen-oxygen isotope geochemical analysis of the samples of Calin-type of gold deposits,northwest of Guangxi, show that the aqoeous solution of this type deposits in the process of ore-forming is mainly basin thermal brine, and metallogenic process has given priority to atmospheric precipitation, with a small amount of magmatic water and metamorphic solution or stratum water admixed.9. The research of S-Pb-C stable isotope and wallrock alteration, ore characteristics, fluid inclusions, magmatic activities and ancient geothermal field of the main deposits in northwest guangxi, determine that the metallogenic material such as gold of Calin-type of gold deposits in this area mainly come from the mineral of mainland basin layer, where exist a set of source bed with relatively abundant metallogenic material.The sulfur of ore mainly comes from wallrock formation,while partly from organic matter of stratum and resourse of deep. All these features show that the lead of GaoLong mining area mainly comes from the upper crust, namely sedimentary rock formation,and partly from the orogenic belt, in conclusion that the lead is predominate stratum resoures,while mixed with a bit of leac of orogenic belt in deep.lO.This system study the guide ore structure and ore space of the Carlin-type gold deposits which is located in the northwest of Guangxi. The mineralization and space-time distribution of Carlin-type gold deposits are controlled by the region multistage and various types of structure.In the regional range, the region is located in the combining site of Yangtze paraplatform and the south rim of the south china fold system,its tectonic structure position is in the edge of the plate tectonic; the deep and large scale fault structure of the northwest of Guangxi is very developing, such as Youjiang fault, Nandan-KunLunguan fault, Tianlin-Bama fault and Bama-Leye concealed fault, etc, which control the formation of Youjiang basin and gold ore belt. The edge of ancient land is tectonic weak zone in the crust and the window and channel of crust-mantle whose boundary is in open state. Two way exchange of material between the crust and the mantle,the active of mixing action and the strong of energy exchange and switching action,the frequent of tectonic movement and the significant of diagenesis and mineralization often can form various metallogenic system in the edge of ancient land.11.This paper will discuss every stratum unconformity surface and the significance of ore-controlling in the region of the northwest of Guangxi. In the mining area within the range, there are more than5stratum such as D-∈、C1-D3、P2-Pi、T1-T2and T2-T2whose unconformity surface as well as its composite fault, insequent fault, interformational broken belt, which control this Carlin-type gold deposits regularities of distribution and the output location of ore body. Ore body whose shape is stratoid, leticular and the combination of Rattan melon is chiefly located in the sedimentation surface of discontinuity, A little of ore body whose shape is veined and stratoid is located in the hanging wall of the surface of discontinuity or interformational broken belt.12.It is the leading factor that the ore-forming geological ensure the metallogenic model. This Carlin-type gold deposits based on the forming process and metallogenic model can be divided into initial gathered period, basin fluid phase, mineralization period and supergene weathering period. 13.This system had summaried the geological factors of ore-controlling which belongs to the region of the northwest of Guangxi, putted forward five metallogenic forecasting areas, summaried the metallogenic model of forecasting area and prospecting marks, putted forward delineation of method and principle of forecasting area and defined the forecasting target area.