GENESIS AND PRODUCTS OF REPLACEMENT OF TOCHILINITE AND VALLERIITE IN SULFIDE-BEARING BORATE ORES OF MAGNESIAN SKARN DEPOSITS

Abstract

Tochilinite, valleriite, and associating minerals were studied in borate ores from the gold-copper magnesian skarn deposits of Transbaikalia and North Korea and calciphyre of Yakutia. It was shown that the appearance of endogenic bruche in association with Fe and Cu sulfides at the szaibelyitization of magnesioludwigite is a necessary and sufficient condition of their formation. The occurrence of brucite in altered periclase marbles, calciphyres, and serpentinized forsterite skarns in the presence of sulfides is also favorable for the formation of tochilinite and valleriite. The hydroxosulfides show variable compositions both in the sulfide and hydroxide constituents of their mixed-layer crystal structure. It was demonstrated that the development of hydroxosulfides in szaibelyitized magnesioludwigite ores is a negative factor promoting boron migration and depreciating the value of the ore. The occurrence of valleriite in Au-Cu ores results in losses during their floatation. The typomorphism of Fe and Cu hydroxosulfides was considered in B, Cu, and Au deposits, and their potential positive role was discussed in the supergene migration of Au and the formation of Au placers.