The Characteristic Of Carbon Isotope And Mineralization Significance Of Black Alteration Of Baimadong U-polymetallic Deposit

Baimadong U-polymetallic deposit is located in Bamadong region,Kaiyang country,Guizhou province and belongs to the SW margin of the Yangzi Landmass.Baimadong ore district has well-developed fault and poor-developed fold.It has go through multi-period alteration,which has all kinds of types.Firstly,the main kinds of alteration are silicification and black alteration.Secondly,the kinds of alteration are baratization,clayization,reddening,calcitization,fluoritization,baratization.Among all kinds of types,the black alteration is an unique alteration and is closely related to uranium mineralization.Therefore,discussing and finding out the composition of black alteration,especially the source of organic matter has important denotative meaning for prospecting in deep and peripheral district.Through researching the geochemical characteristics of total organic carbon and inorganic carbon,isotope of organic carbon and inorganic carbon,trace elements of samples from Baimadong U-polymetallic deposit and combining microscopic observation,reach the following understanding:?1?The test results of total organic carbon is:black altered rocks>red altered rocks>unaltered rocks.Sample gathered from source bed of uranium has the highest level of total organic carbon.These results prove that alteration brings amount of organic matter.Uranium mineralization has close relationship with black alteration and organic matter.What's more,the total amount of sulfur and organic carbon have positively correlated relationship,that is total amount of sulfur meet the following law:black altered rock>red altered rock>unaltered rock.This means those samples which have high level of organic matter,also have high level of sulfur.According to this,I conclude that the source of sulfur has biological sulfur.?2?The amount of chloroform bitumen"A"?soluble organic carbon?is low,so it can be classified into non-source beds.This outcomes can testify that organic matter in black altered rocks has go through a higher mature evolution.?3?The test results of total inorganic carbon show that total inorganic carbon of altered rocks?remove samples that contains calcite?is far lower than that in no-altered rocks.This outcome shows that alteration has changed the ingredient of protodolomite and making its main ingredient are not CaMg[CO₃]₂.?4?The test results of organic carbon isotope show that samples are higher in light isotope12C than standard.What's more,excepting sample NTT,which gathered from source bed of uranium----Niutitang formation,the rest 13 samples have similar characteristics in organic carbon isotope.Their range of variation is-29.7‰^-25.0‰,conforming with the range of organic carbon isotope of sedimentary rocks metamorphic rocks igneous rocks and has smaller change.This outcome shows that the source of organic matter is consistent.The value of organic carbon isotope of the 13samples is different with that in source bed of uranium,which is-33.0‰.They have big difference.This outcome proves that the source of uranium is not source bed of uranium-Niutitang formation.Thinking the organic matter comes from surface.The value of?¹³Corg of sapropel-type kerogen is-28.2^-32.2‰,researched region has similar value with this range.So I conclude that organic matter comes from marine alga plankton and the type of organic matter is type I kerogen.?5?In this paper we research 14 samples,but only 6 of them got outcomes of?¹³C and?¹⁸O through experiment.Excepting NTT sample?mudstone,comes fromNiutitang formation?,the rest 8 samples which cannot get the outcome of?¹³C and?¹⁸O are altered.This outcome can also show that alteration has changed ingredient of protolith thoroughly.The range of?¹³C is big and this can prove that it has various source.According to the source of carbon in hydrotherm,Thinking the researched object has both source of marine sedimentary carbon and hydrothermal carbon.Among the two kinds of source,the latter one is the outcome of alteration.The value of?¹³C and?¹⁸O of the 6 samples is lower,this outcome is closely related to the exist of organic matter.Because the CO₂ released from pyrolysis by organic matter is rich in ¹²C and this kind of CO₂ have buffer action to CO₂ in hydrotherm,which is rich in ¹³C.This is one of the reason that leads to the value of?¹³C lower.?6?The relevance of U,Th,Organic matter show that all kinds of rocks have been through hydrothermal process,the only difference is the intensity.The hydrothermal process has the strongest power to black altered rock and then is red altered rock,protolith.The value of U?Th is different in black altered rock and sedimentary rock,this outcome shows that it has been through hydrothermal process.?7?Distribution mode of REE shows that the source of hydrothermalism fluid is consistent.Anomaly of Eu is not obvious.It is rich in LREE.The degree of fractionation of LREE is higher.Compared with LREE,the degree of fractionation of HREE is lower.Eu shows negative anomaly and Ce is stable relatively.This can conclude that they formed in reductive environment.