Rhenium in Molybdenite: a Database Approach to Identifying Geochemical Controls on the Distribution of a Critical Element Item Type Article Authors Barton, Isabel F.; Rathkopf, Christian A.; Barton, Mark D. Citation Barton, I. F., Rathkopf, C. A., & Barton, M. D. (2019). Rhenium in Molybdenite: a Database Approach to Identifying Geochemical Controls on the Distribution of a Critical Element. Mining, Metallurgy & Exploration, 1-17. DOI 10.1007/s42461-019-00145-0 Publisher Springer Science and Business Media LLC Journal MINING METALLURGY & EXPLORATION Rights © Society for Mining, Metallurgy & Exploration Inc. 2019. Download date 02/10/2021 13:24:48 Item License http://rightsstatements.org/vocab/InC/1.0/ Version Final accepted manuscript Link to Item http://hdl.handle.net/10150/636269 Manuscript Click here to access/download;Manuscript;Manuscript_ReMolyDatabase_MM Click here to view linked References 1 2 3 4 1 Rhenium in molybdenite: A database approach to identifying geochemical controls 5 6 7 2 on the distribution of a critical element 8 9 3 Isabel F. Barton 1, 2, ,3 , Christian A. Rathkopf 4,5, Mark D. Barton 2, 4 10 11 12 4 13 14 5 1 Corresponding author: [email protected] 15 16 6 2 University of Arizona Lowell Institute for Mineral Resources 17 18 19 7 3 now with University of Arizona Department of Mining and Geological Engineering, 20 21 8 1235 James E. Rogers Way, Tucson, AZ 85721 22 23 4 th 24 9 University of Arizona Department of Geosciences, 1040 E. 4 St., Tucson, AZ 85721 25 26 10 5 now with Hecla Mining, 3300 Traders Way, Suite C, Box 15, Winnemucca, NV 89445 27 28 29 11 30 31 12 Abstract 32 33 34 13 Molybdenite is the world’s principal source of rhenium (Re), a critical element in 35 36 14 multiple high-tech applications. However, the Re contents in molybdenite vary by orders 37 38 15 of magnitude on scales ranging from single grains to whole deposits. In order to better 39 40 41 16 understand the systematics of this variation and what geochemical factors control 42 43 17 molybdenite Re concentration, and hence overall Re resources, we examine global 44 45 46 18 patterns in molybdenite Re contents through a compilation of > 3,000 measurements of 47 48 19 Re in molybdenite from > 700 mainly ore-bearing moderate- to high-temperature 49 50 51 20 hydrothermal systems of different types. Our results are similar to but expand on those of 52 53 21 earlier studies. 54 55 22 Rhenium concentration in molybdenite has a lognormal distribution in 56 57 58 23 molybdenites and varies systematically with type of geologic system, intrusive lithology, 59 60 61 62 63 1 64 65 1 2 3 4 24 and Mo grade. The lowest-Re molybdenite occurs in greisens (geometric mean 1 ppm ± a 5 6 7 25 multiplicative standard deviation of 9), quartz vein-hosted W-Sn deposits (2 ± 5 ppm), 8 9 26 unmineralized granites and granodiorites (12 ± 8 ppm), intrusion-related deposits (14 ± 8 10 11 12 27 ppm), and porphyry W-Sn deposits (16 ± 11 ppm). Rhenium is most enriched in 13 14 28 molybdenites from volcanic sublimates (23,800 ± 5 ppm), with skarn Fe and Au (560 ± 5 15 16 29 ppm and 540 ± 3 ppm respectively) and porphyry Cu and Cu-Au deposits next (470 ± 4 17 18 19 30 and 430 ± 7 ppm respectively). Among porphyries, skarns, and quartz vein-hosted 20 21 31 deposits, Re is most highly concentrated in molybdenites from Cu and Au systems and its 22 23 24 32 concentration decreases systematically through Cu-Mo, Mo, Sn, and W deposits. In 25 26 33 nearly all cases, molybdenites from systems associated with intermediate igneous rocks 27 28 29 34 contain more Re than molybdenites from systems of the same type with more felsic rock 30 31 35 associations. The disparity between Re contents of molybdenite infelsic and intermediate 32 33 34 36 systems is largest for porphyries, quartz vein-hosted, and skarn deposits and is near zero 35 36 37 for subeconomic or barren granite and granodiorite Mo systems; felsic intrusion-related 37 38 38 deposits have slightly higher molybdenite Re than their equivalents associated with 39 40 41 39 intermediate intrusions. In most systems molybdenite Re content does not correlate with 42 43 40 metal grade, but may have an inverse correlation with Au grade in intrusion-related 44 45 46 41 deposits (based on a small number of data points) and does exhibit a strong inverse 47 48 42 correlation with deposit Mo grade. Dilution of Re through larger amounts (higher deposit 49 50 51 43 grades) of molybdenite explains about 40% of this correlation, but the relative 52 53 44 enrichment of Re in molybdenite from low-Mo deposits must also reflect some selective 54 55 45 enrichment of Re:Mo in porphyry Cu systems compared to porphyry Mo systems. We 56 57 58 46 found no evidence for secular increase or other systematic temporal variation in 59 60 61 62 63 2 64 65 1 2 3 4 47 molybdenite Re content. The data regarding the use of molybdenite Re content as a proxy 5 6 7 48 for mantle influence are ambiguous. 8 9 49 Nearly all observed empirical correlations can be traced back to differences in 10 11 12 50 redox state and sulfide concentration, the two geochemical factors identified here and by 13 14 51 previous experimental work as the controlling influences on Re mobility under 15 16 52 hydrothermal conditions. Hydrothermal systems with reducing conditions (W- and Sn- 17 18 19 53 rich) tend to have low molybdenite Re even though compiled whole-rock data indicate 20 21 54 that their source rocks have as much or more Re as those of more oxidized systems (e.g., 22 23 24 55 Cu-rich). Vapor-phase exsolution, crustal assimilation, and mixing with external fluids, 25 26 56 may all enrich molybdenite Re concentrations in individual deposits and deposit types, 27 28 29 57 but their extent and importance in overall hydrothermal concentration of Re is uncertain. 30 31 58 Thus, it appears that the available molybdenite Re resource in an ore deposit largely 32 33 34 59 depends on how the deposit’s redox and sulfidation conditions have varied over time and 35 36 60 space during the timespan of hydrothermal activity. Oxidized, high-sulfide conditions 37 38 61 tend to concentrate Re in molybdenite, whereas reducing conditions tend to leave Re 39 40 41 62 dispersed at low concentrations in the bulk rock. 42 43 63 keywords: rhenium, molybdenite, Re-Os, porphyry deposits, exploration, rhenium 44 45 46 64 behavior in hydrothermal systems 47 48 65 49 50 51 66 1. Introduction 52 53 67 1.1 Background and purpose of this study 54 55 68 Rhenium is an essential element in the manufacture of superalloys, turbine blades, 56 57 58 69 and various catalysts used in refining petroleum. While U.S. reserves of rhenium are 59 60 61 62 63 3 64 65 1 2 3 4 70 substantial, Re is a designated critical element in the U.S. due to limited production, low 5 6 7 71 recycling capability, and heavy reliance on imports (John et al., 2017 [1]).The vast 8 4+ 9 72 majority of Re is produced as a byproduct of molybdenite (MoS2), where Re substitutes 10 11 4+ 12 73 for Mo ; end-member rheniite ReS2 is extremely rare (John and Taylor, 2016 [2]). 13 14 74 However, Re concentrations in natural molybdenite vary over nearly 9 orders of 15 16 75 magnitude from tens of % to a few parts per billion, and over scales from a single grain to 17 18 19 76 a whole deposit (Rathkopf et al., 2017 [3]). Despite several attempts (e.g. John and 20 21 77 Taylor, 2016 [2]; Giles and Schilling, 1972 [4]; Terada et al., 1971 [5]; Newberry, 1979 22 23 24 78 [6]; Berzina et al., 2005 [7]; Voudouris et al., 2013 [8]; Ciobanu et al., 2013 [9]), no 25 26 79 consistent pattern to this variability has been discovered, nor has any geochemical 27 28 29 80 rationale for why Re content in molybdenite varies so much. 30 31 81 To address this question, we compiled a database of Re concentrations measured 32 33 34 82 from molybdenites in mineralized and unmineralized sites, most of them hydrothermal. 35 36 83 Our goal in this compilation is to identify patterns that will enable us to evaluate what 37 38 84 geochemical factors control the Re content of molybdenites and to assess whether 39 40 41 85 molybdenite Re content can reliably be used as a vector to ore deposits or to high grades, 42 43 86 as has been previously suggested (e.g. Berzina et al., 2005 [7]; Voudouris et al., 2013 [8]; 44 45 46 87 Coope, 1973 [10]; Voudouris et al., 2009 [11]). Given this focus on molybdenite Re 47 48 88 contents, we only touch on the Re(-Mo) enrichments present in many sediment-hosted Cu 49 50 51 89 and U systems, which are well known but which have not been definitively traced to Re- 52 53 90 rich molybdenite (John et al., 2017 [1]). 54 55 91 Compilations of molybdenite Re content have been made before (discussion 56 57 58 92 below), but most have included <100 data points. Although these are valuable 59 60 61 62 63 4 64 65 1 2 3 4 93 contributions, the number of data points per deposit type, rock type, or region is 5 6 7 94 comparatively small.