Study Of Geology And Geochemistry Of The Low-temperature Hydrothermal/epithermal Deposits

This article systematically studied two hydrothermal deposits,namely the gold deposits in Guizhou,China and the uranium deposit in Mika,Nigeria.The gold deposits are of the orogenic type,also known as the turbidite-hosted gold deposits.They bear all the special features of the turbidite deposits such as big and native gold granules,large reserve,less associated minerals,related to anticlines,structural dependent,as a typical orogenic-hydrthermal deposit.From the chronological analysis,the rocks in the strata were dated to the period of 800 Ma.The area was originally of a sea bed under a drastic environment surrounded by a range of volcanos at the edge of a subduction boundary or continental margin based on geochemistry and geology evidence,white and black chimneys(or hot springs)emitted quartz and ferro-manganese fluids which cooled down to form nodules spasmodically in the nearby area.The gold mineral was enriched under multi-stages of geological activities mostly as Xufeng tectonic movement within a confined area that produced gold and barite as the two economic products in Tian Zhu of Guizhou province,which is known as the "Gold Capital of the plateau" and the largest barite mine of China.Based on geological,geochemical,geochronological studies on the Chaoyangzhai gold deposit,we draw the following conclusions for the source of the gold as follows,(1)LA-ICP-MS zircon U-Pb dating of the gold-bearing quartz,tuffaceous-and sandy-slates display similar characteristics of age distribution,indicating that the zircons in the gold-bearing quartz could originate from the surrounding tuffaceous-and sandy-slates.(2)Rocks of the Qingshuijiang Formation might be sourced from a felsic igneous provenance.(3)Similar geochemical patterns between the surrounding tuffaceous-and sandy-slate and gold-bearing quartz illustrate that the Chaoyangzhai gold deposit might be sourced from the surrounding tuffaceous-and sandy-slate,supported by the sulfur isotopes of the arsenopyrite and pyrite.(4)Sandy-slates have higher Au contents than the tuffaceous slate,indicating that gold might be sourced from the sandy-slate rather than tuffaceous slate.(5)The gold-bearing quartz veins yielding similar age distributions,indicating that zircon grains in gold-bearing quartz veins were originated from the surrounding tuffaceous-and sandy-slates which were sourced from a felsic igneous provenance in Neoproterozoic.The metamorphic devolatilization,caused by the Caledonian orogeny(Xuefeng Orogenic Event),resulted in the formation of the ore-forming fluid.Uranium exploration was conducted especially in currently non-producing countries like Nigeria with high economic prospect.This study investigates a new uranium prospect in Mika,Northeastern Nigeria.The Mika uranium mineralization is located in Mika,Taraba State.Two lodes were identified and additional nine trenches were performed.The main lode in the west extends about 10m,ore vein strikes 348°,inclination 420 and the strike of the lode 3060 with average uranium content of 18%;the eastern trench is about 8x4x6m,and exposes a veinlet of pitchblende.From the petrography one can deduce that the granitic host rock has suffered deformation which resulted in the crushing of quartz crystals and stretching of plagioclase.The uraninite and chalcedony in the late phase filled up the fractures along the crystal grain boundaries as veinlets.The laboratory gamma ray analysis of the samples showed that the secondary uranium content is 0.1%,while the primary uranium ore grade is 1.5%.Radiometric in-situ measurements showed Th and K ranges around 47.3-3654 ppm and 4.26-6.26%.From the survey,a strong radiometric zone extends 800x35m in a NW-SE direction and has the highest radiation content 1200cpm against background count rate of 30cpm.Generally,the uranium concentrations in the ores in Mika area range from 0.03%-0.12%.Since only the surface occurrences have been explored,the area studied would be a good prospect for future development if it is properly explored.During the uranium survey,4-channel gamma spectrometers and gamma dosimeters were used,and a radiometric map was prepared.The natural nuclides were tested through the low level HPGe gamma spectrometer in the laboratory.As the result,some significant radioactive points were located.