Mineralogical and geochemical features of bismuth in Proterozoic ore-bearing structures of west part of the Ingul megablok (Ukrainian shield)

Abstract

In this paper we summarize the geological information about regional distribution features of bismuth in the Ingul megablok of Ukrainian shield. Different Proterozoic ore sites situated within the Bratsk-Zvenihorodka and the Ingul-Tyasmyn metallogenic zone are considered. They are characterized by the presence of various scale deposits of uranium, rare metals (Li, Rb, Cs, Ta, Nb, W, Sn) and precious metals (Au, Ag). Minerals-concentrators of bismuth and main paragenetic associations comprising native Bi, tellurides, bismutite, maldonite, wittichenite, parkerite, matildite are investigated. It should be noted that within the intrusions of the Korsun-Novomyrgorod pluto and the Novoukraika massif, which spatially separate the Bratsk-Zvenihorodka and the Ingul-Tyasmyn metallogenic zone, there are also deposits of uranium and titanium, but bismuth is practically absent. At a relatively low content (from 5 to 60 g / t) bismuth is a typical metal for ore objects of K-U formation and rare metal pegmatites of Polokhiv and Stankuvatske ore fields. For the first time, mineral forms of bismuth (native bismuth, Pb-bismuth, galenobismuthin) were determined in the Obginnyi ore occurence, where abnormally high content values of bismuth up to 0,8-1,3%. The geochemical feature of numerous gold ore objects is the almost complete dominance of bismuth compounds with tellurium. There are headleite (Ві7Те3), telluric bismuthite (Ві2Те3), tsumoit (ВіТе), pilsenite (Ві4Те3), joseite-B (Bi4(S,Te)3) detected individualized phases in the Bi-Te system. In the skarns of the Bandurkivsky ore occurence the early productive association consists of maldonite + joseite-B + tetradimite, and the late one consists of native gold + bismuth. Bismuth sulfosalts are present in various ore objects as part of sulfide Cu-Ag-Bi and Pb-Ag-Bi mineralization. The study of geochemistry and mineralogy of bismuth was performed in M.P. Semenenko institute of geochemistry, mineralogy and ore formation of NAS of Ukraine, using a scanning electron microscope JSM-6700F (JEOL). Data on the chemical composition of minerals were obtained using microprobe devices JCXA-733, JXA-8200 (Technical Center of the National Academy of Sciences of Ukraine) and Cameca SX-100 (Technical University, Klausstal (Germany)). The data of spectral and atomic absorption analysis of the central laboratory of KP «Kirovgeologiya» were also used in writing the article.