Crystal Growth through the Medium of Nonautonomous Phase: Implications for Element Partitioning in Ore Systems
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TAL GROWTH Dedicated to the memory of Vadim Sergeevich Urusov
Crystal Growth through the Medium of Nonautonomous Phase: Implications for Element Partitioning in Ore Systems V. L. Tausona,b,*, S. V. Lipkoa, K. Yu. Arsent’eva,c, and N. V. Smagunova a Vinigradov
Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia Irkutsk Scientific Center, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia c Institute of Limnology, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail: [email protected] b
Received May 23, 2017; revised January 10, 2018; accepted January 24, 2018
Abstract—The phenomena related to the crystal growth in close-to-natural multicomponent systems have been considered. It is shown that the distribution of rare-earth elements in magnetite and hematite and the distribution of noble metals (NMs) in pyrite and magnetite are controlled by surficial nonautonomous phases (SNAPs). The increase in the fractionation and cocrystallization coefficients of elements is related to the presence of these phases. The dependence of SNAPs on the physicochemical growth conditions suggests typomorphism of mineral surfaces. The SNAP evolution during crystal growth explains some specific features of mineral growth systems, in particular, the existence of highly determinate dependences of uniformly distributed incompatible element admixture on the specific surface area of crystal, as well as the formation of nano- and microinclusions and microzonality in crystals. The results obtained are important for the ore formation theory and the practical estimation of the economic potential of ore deposits in view of determining the “hidden” metal content and elaborating a rational technology to recover ore material resources. DOI: 10.1134/S1063774519030271
INTRODUCTION Mineral associations have a number of specific features that are difficult to explain. However, the adequacy of the methods (both experimental and computational) developed for simulating the mineral formation without understanding the nature of such features appears questionable. Until now, it is unclear why multiphase mineral associations that do not obey the Phase Rule even in its extended versions [1, 2] exhibit stability under natural conditions during geological periods of time (millions, tens of millions, and hundreds of millions years). This is especially true for the so-called microparageneses, consisting of micrometer-sized mineral crystals. It is difficult to explain the occurrence of such associations as a result of unified growth process, because it is unclear how components are selected during growth of a specific individual in this multiphase system. Unfortunately, the growth practice does not help much to solve this problem. In contrast to geochemists, which are interested in the processes occurring in complex systems (multisystems), “…crystal growers view modifying agents as unwanted impurities and work extremely hard to eliminate them from the starting materials” [3]. As a con-
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