The Dal'negorsk borosilicate skarn deposit, primorye, Russia: Composition of ore-bearing solutions and boron sources

The Dal'negorsk borosilicate skarn deposit (44A degrees 34' N and 135A degrees 37' E), located in the center of the ore field bearing the same name, is referred to the category of giant deposits. The currently predominant genetic concept assumes that ore mineralization at this deposit is related to a mantle source and that boron and ore-bearing alkaline fluids are derivatives of a juvenile source as well. The alternative model considered in this paper suggests that sedimentary sequences, probably, evaporites of a local basin, were immediate boron sources and hot subsurface water served as an agent of ore deposition. The authors' conclusions are based on (1) mineralogical and geochemical features of alteration of premineral dikes as evidence for the composition of percolating ore-bearing fluids, (2) results of fluid inclusion study, and (3) boron and oxygen isotopic compositions of datolite. The latite bodies immediately predating deposition of economic datolite ore do not show mineralogical or geochemical attributes of their belonging to alkaline rock series. According to our data, these bodies are composed of Paleogene premineral basalts that intruded into the future borosilicate deposit close to the central channel of ore-bearing fluid, served as fluid conduits, and were altered to ultrapotassic rocks under the effect of such fluid. It is suggested that hot aqueous ore-bearing fluid was enriched in highly soluble compounds of Ba, K, and B and extremely depleted in poorly soluble compounds of Zr, Nb, Ta, La, and Ce. This suggestion does not contradict the properties and composition of primary and pseudosecondary two-phase fluid inclusions in danburite, datolite, quartz, and fluorite from orebodies. Judging from the boron isotopic composition of datolite (delta B-11 = -9 to -31 aEuro degrees), the main amount of boron was extracted from metasedimentary rocks of the Mesozoic basement. The oxygen isotopic composition of datolite from the Dal'negorsk deposit (delta O-18(SMOW) = -1.64 to -2.97 and less frequently up to -5aEuro degrees) indicates a significant contribution of subsurface water to the transport of boron. A model of multistage accumulation of boron in ore of the Dal'negorsk borosilicate skarn deposit is proposed.