Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona

Christian Rathkopf, Frank Mazdab, Isabel Barton, Mark D Barton

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Electron microprobe analysis of Re concentration in molybdenite grains in 45 samples from 11 rock units at the Bagdad porphyry Cu-Mo deposit found high variability from the grain to the deposit scale. Measured Re concentrations range from < 15 to 4450 ppm and do not correlate with rock unit, age, alteration type, ore grade, proximity to ore, or other observed geological feature. Variability within samples and within grains is nearly as high as variability over the deposit. Within 23 grains of molybdenite from a single 2-cm-long sample, Re content varied from < 15 to 1215 ppm Re. Within single grains the Re content ranges just as widely (e.g. 20 analyses on one grain vary from 44 to 2061 ppm), with intra-grain relative standard deviation (RSD) typically > 0.5 and in some cases > 1. Although microprobe maps show that the Re variation in some crystals correlates with growth-related zoning to a limited extent, there was no pattern to the variation in most of the molybdenite grains and the few zoned examples had no clear sector or consistent oscillatory textures. Based on our current understanding of trace element incorporation during hydrothermal molybdenite growth, this evidently heterogeneous distribution of Re in molybdenite precludes the use of microprobe spot measurements of Re as a vector to mineralization, which was the original focus of this study. A follow-up analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using spot diameters of 150 μm reduced the observed intra-grain variability from 1.67 to 1 order of magnitude, but still failed to yield data that correlated with any known geological features. This suggests that any further work toward using molybdenite Re content as a vector to mineralization should either focus on whole-grain methods of analysis or else should use detailed microprobe mapping of molybdenite growth zones to guide point analyses, and then correlate the growth zones in molybdenite samples taken over distance through the deposit. This approach could help shed light on how the development of heterogeneous Re concentrations on the micro-scale relates to the processes of molybdenite precipitation and alteration.

Original languageEnglish (US)
Pages (from-to)45-54
Number of pages10
JournalJournal of Geochemical Exploration
Volume178
DOIs
StatePublished - Jul 1 2017

Fingerprint

molybdenite
porphyry
Deposits
Inductively coupled plasma mass spectrometry
Zoning
Trace Elements
Electron probe microanalysis
Laser ablation
mineralization
Textures
Rocks
distribution
geological feature
Crystals
ablation
electron probe analysis
zoning
mass spectrometry
laser
texture

Keywords

  • Bagdad
  • Molybdenite
  • Porphyry deposits
  • Rhenium

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Economic Geology

Cite this

Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona. / Rathkopf, Christian; Mazdab, Frank; Barton, Isabel; Barton, Mark D.

In: Journal of Geochemical Exploration, Vol. 178, 01.07.2017, p. 45-54.

Research output: Contribution to journalArticle

@article{4d53613733ac440ebc073077dfcd3f43,
title = "Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona",
abstract = "Electron microprobe analysis of Re concentration in molybdenite grains in 45 samples from 11 rock units at the Bagdad porphyry Cu-Mo deposit found high variability from the grain to the deposit scale. Measured Re concentrations range from < 15 to 4450 ppm and do not correlate with rock unit, age, alteration type, ore grade, proximity to ore, or other observed geological feature. Variability within samples and within grains is nearly as high as variability over the deposit. Within 23 grains of molybdenite from a single 2-cm-long sample, Re content varied from < 15 to 1215 ppm Re. Within single grains the Re content ranges just as widely (e.g. 20 analyses on one grain vary from 44 to 2061 ppm), with intra-grain relative standard deviation (RSD) typically > 0.5 and in some cases > 1. Although microprobe maps show that the Re variation in some crystals correlates with growth-related zoning to a limited extent, there was no pattern to the variation in most of the molybdenite grains and the few zoned examples had no clear sector or consistent oscillatory textures. Based on our current understanding of trace element incorporation during hydrothermal molybdenite growth, this evidently heterogeneous distribution of Re in molybdenite precludes the use of microprobe spot measurements of Re as a vector to mineralization, which was the original focus of this study. A follow-up analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using spot diameters of 150 μm reduced the observed intra-grain variability from 1.67 to 1 order of magnitude, but still failed to yield data that correlated with any known geological features. This suggests that any further work toward using molybdenite Re content as a vector to mineralization should either focus on whole-grain methods of analysis or else should use detailed microprobe mapping of molybdenite growth zones to guide point analyses, and then correlate the growth zones in molybdenite samples taken over distance through the deposit. This approach could help shed light on how the development of heterogeneous Re concentrations on the micro-scale relates to the processes of molybdenite precipitation and alteration.",
keywords = "Bagdad, Molybdenite, Porphyry deposits, Rhenium",
author = "Christian Rathkopf and Frank Mazdab and Isabel Barton and Barton, {Mark D}",
year = "2017",
month = "7",
day = "1",
doi = "10.1016/j.gexplo.2017.03.011",
language = "English (US)",
volume = "178",
pages = "45--54",
journal = "Journal of Geochemical Exploration",
issn = "0375-6742",
publisher = "Elsevier",

}

TY - JOUR

T1 - Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona

AU - Rathkopf, Christian

AU - Mazdab, Frank

AU - Barton, Isabel

AU - Barton, Mark D

PY - 2017/7/1

Y1 - 2017/7/1

N2 - Electron microprobe analysis of Re concentration in molybdenite grains in 45 samples from 11 rock units at the Bagdad porphyry Cu-Mo deposit found high variability from the grain to the deposit scale. Measured Re concentrations range from < 15 to 4450 ppm and do not correlate with rock unit, age, alteration type, ore grade, proximity to ore, or other observed geological feature. Variability within samples and within grains is nearly as high as variability over the deposit. Within 23 grains of molybdenite from a single 2-cm-long sample, Re content varied from < 15 to 1215 ppm Re. Within single grains the Re content ranges just as widely (e.g. 20 analyses on one grain vary from 44 to 2061 ppm), with intra-grain relative standard deviation (RSD) typically > 0.5 and in some cases > 1. Although microprobe maps show that the Re variation in some crystals correlates with growth-related zoning to a limited extent, there was no pattern to the variation in most of the molybdenite grains and the few zoned examples had no clear sector or consistent oscillatory textures. Based on our current understanding of trace element incorporation during hydrothermal molybdenite growth, this evidently heterogeneous distribution of Re in molybdenite precludes the use of microprobe spot measurements of Re as a vector to mineralization, which was the original focus of this study. A follow-up analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using spot diameters of 150 μm reduced the observed intra-grain variability from 1.67 to 1 order of magnitude, but still failed to yield data that correlated with any known geological features. This suggests that any further work toward using molybdenite Re content as a vector to mineralization should either focus on whole-grain methods of analysis or else should use detailed microprobe mapping of molybdenite growth zones to guide point analyses, and then correlate the growth zones in molybdenite samples taken over distance through the deposit. This approach could help shed light on how the development of heterogeneous Re concentrations on the micro-scale relates to the processes of molybdenite precipitation and alteration.

AB - Electron microprobe analysis of Re concentration in molybdenite grains in 45 samples from 11 rock units at the Bagdad porphyry Cu-Mo deposit found high variability from the grain to the deposit scale. Measured Re concentrations range from < 15 to 4450 ppm and do not correlate with rock unit, age, alteration type, ore grade, proximity to ore, or other observed geological feature. Variability within samples and within grains is nearly as high as variability over the deposit. Within 23 grains of molybdenite from a single 2-cm-long sample, Re content varied from < 15 to 1215 ppm Re. Within single grains the Re content ranges just as widely (e.g. 20 analyses on one grain vary from 44 to 2061 ppm), with intra-grain relative standard deviation (RSD) typically > 0.5 and in some cases > 1. Although microprobe maps show that the Re variation in some crystals correlates with growth-related zoning to a limited extent, there was no pattern to the variation in most of the molybdenite grains and the few zoned examples had no clear sector or consistent oscillatory textures. Based on our current understanding of trace element incorporation during hydrothermal molybdenite growth, this evidently heterogeneous distribution of Re in molybdenite precludes the use of microprobe spot measurements of Re as a vector to mineralization, which was the original focus of this study. A follow-up analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using spot diameters of 150 μm reduced the observed intra-grain variability from 1.67 to 1 order of magnitude, but still failed to yield data that correlated with any known geological features. This suggests that any further work toward using molybdenite Re content as a vector to mineralization should either focus on whole-grain methods of analysis or else should use detailed microprobe mapping of molybdenite growth zones to guide point analyses, and then correlate the growth zones in molybdenite samples taken over distance through the deposit. This approach could help shed light on how the development of heterogeneous Re concentrations on the micro-scale relates to the processes of molybdenite precipitation and alteration.

KW - Bagdad

KW - Molybdenite

KW - Porphyry deposits

KW - Rhenium

UR - http://www.scopus.com/inward/record.url?scp=85017175222&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85017175222&partnerID=8YFLogxK

U2 - 10.1016/j.gexplo.2017.03.011

DO - 10.1016/j.gexplo.2017.03.011

M3 - Article

VL - 178

SP - 45

EP - 54

JO - Journal of Geochemical Exploration

JF - Journal of Geochemical Exploration

SN - 0375-6742

ER -