NEW DATA ON GEOCHEMISTRY AND GENESIS OF THE SPETSUGLI GERMANIUM-COAL DEPOSIT (PRIMORSKY KRAI)

Abstract

The relevance of this research is conditioned by the need to develop predictive and prospecting criteria for identifying a strategically important type of germanium raw material – germanium-coal deposits. The main aim is to study the geochemical features and conditions for the formation of complex rare-metal mineralization in coals of the Spetsugli deposit (Far East) and by this example develop a geological-geochemical model of the formation of deposits of similar type. Objects: coal, coal-bearing rocks, underground waters and basement rocks of the germanium-coal deposit. Methods: geological and geochemical sampling, inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, scanning electron microscopy, optical microscopy, X-ray phase analysis, correlation analysis. Results. New data on the geological structure and geochemistry of coals and coal-bearing rocks in the Spetsugli germanium-coal deposit in the Primorsky Krai were obtained. The complex polyelement composition of rare-metal mineralization in the deposit is explained. It is consistent with geochemistry and minerageny of basement rocks and the framing of the Pavlovsk depression. Anomalously high concentrations of Ge, Sb, Hg, W, Li, Be, Cs, and As are typical in metalliferous coals; they are tens and hundreds of times higher than the average content in lignite worldwide. The accumulation levels of U, Mo, Y, Rb, REE, Zn and Ga are somewhat less anomalous. The complex mineralogical-geochemical and geological-structural analysis of the composition and structure of the Spetsugli Ge-coal deposit made it possible to reevaluate the accepted hydrothermal model of Ge mineralization in coals. It also helped to validate the previously proposed hypergene model, which states that the sources of metals are basement rocks hosting coal deposits. The pre-Cenozoic age of endogenous rare-metal mineralization in granites of the basement was substantiated. The formation of Ge and accompanying mineralization in the Spetsugli deposit was influenced by the forming weathering crust over the rare-metal granite of the Voznesensky complex cut by dikes of the Late Permian age. The deposit is confined to a granite upland, forming a concentric-zonal halo of Ge and associated elements around it. Granites underwent hydrothermal and metasomatic alteration which resulted in quartz-albite-microcline metasomatites and greisens containing W-Mo and Hg-Sb-As mineralization. Rare-metal mineralization in coals is associated with the formation of kaolin weathering crust over granites, removal and redeposition of basic elements in the surrounding peat paleo-bogs in the Paleogene.

Keywords

• germanium-coal deposit
• coal
• geochemistry
• rare elements
• rare-metal mineralization
• conditions of formation
• hydrogenous model