Characteristics And Formation Of Turquoise Of Zhushan County,Hubei Province,China

Turquoise is a kind of precious semi-gem.Two type of rocks were found be able to host turquoise,namely intermediate-acidic volcanic rocks and carbon-bearing siliceous slates.The latter one only occurs at about Zhushan County,Hubei province,China.In this work,we take turquoises and country rocks of Qingu and Wenfeng mine,Zhushan County,Hubei province,China as subjects of study,which are observed by optical microscope and scanning electron microscopy.The characteristics of trace elements of turquoises at these two mines have been analyzed.And the spectral characteristics of turquoise from Zhushan County,Hubei province and Bijishan mine,Anhui province are analyzed by Infrared spectroscopy,as well as Raman spectroscopy.In addition,Cu,H and O isotope results from former researchers have been studied further and the formation mechanism was explored.Turquoise samples from Zhushan County,Hubei province are directly constituted of tiny turquoise crystals,while Turquoise samples of Bijishan mine,Anhui province are aggregated by medium assembly of tiny tabular turquoise crystals.The“pores”in Hubei turquoise are formed because of the tiny crystal absence at certain positions.Anyway,in Anhui turquoise there are tiny turquoise crystals arranging as swirls and absences of cluster tiny crystals,resulting to“pores”.For turquoise,the more advanced shape the tiny crystals have,the more compact the aggregations are.It can be confined via optical microscope that turquoise of Qingu and Wenfeng formed after the low-metamorphic incidents of country rocks.Barites appear in turquoise with and after the formation of turquoise.The curves of REE distribution of Wenfeng mine right dip little and show LREE enrichment with negative Ce anomaly and slight negative Eu anomaly.The curves of REE distribution of Qingu mine left dip and show HREE enrichment with negative Ce anomaly and positive Eu anomaly,indicating lack of Ce of the turquoise ore fluid.Li⁺,K⁺,Na⁺can be compensators for REE to replace Cu²⁺in turquoise,especially Li⁺.And there can be a Al³⁺replacement by Be²⁺?Mg²⁺?Ti⁴⁺?V³⁺?Cr³⁺?Fe²⁺?Fe³⁺?Ga³⁺?Zr⁴⁺?Nb⁵⁺?Ta⁵⁺?Ce⁴⁺.It is unreliable to use ratios of Th/U to testify that turquoise formed in a reducing environment.The kind of turquoise with blue color and great intensity is regarded as high-quality turquoise in this work.We can distinguish high-quality turquoise from Qingu mine,Wenfeng mine,Zhushan County,Hubei Province and Bijiashan mine,Anhui Province by Infrared spectroscopy and Raman spectroscopy.Infrared spectra of the studied samples in this investigation show that peak near 783 cm^-1caused by OH bending vibration of turquoise from Qingu separates into two peaks,797 cm^-1and 779 cm^-1.While the peak appears at 787 cm^-1for turquoises from Wenfeng and783 cm^-1for the ones from Bijiashan.Intensity ratios of infrared absorption peaks at783 cm^-1and 837 cm^-1(R=I^-1_783cm/I^-1_837cm)are different among them.Peaks in Raman spectra around 3500 cm^-1are different among the three locations,namely 3506 cm^-1and 3505 cm^-1for samples from Bijiashan.And the same situation occurs at peak?551 cm^-1.?⁶⁵Cu of turquoise from Qingu and Yungaisi mine,Hubei Province all appear positive ratios,ranging from 0.06‰to 5.08‰.The ones from Wenfeng mine are from-1.28‰to-1.75‰.It's evident that Oxidation reaction and precipitation of crystals from saturated solutions will cause the enrichment of the heavy isotope of Cu.So the positive ratios of?⁶⁵Cu of turquoise result from Oxidation reaction.Turquoise formed by supergene process.Meteoric water can become turquoise ore fluid by flowing underground.There were at least two flows of fluids mixing that causing the precipitation of turquoise,for the properties of fluids changed.Then the precipitation dehydrated to solid turquoise.