TY - JOUR
T1 - Metal anomalies in zircon as a record of granite-hosted mineralization
AU - Gardiner, Nicholas J.
AU - Hawkesworth, Chris J.
AU - Robb, Laurence J.
AU - Mulder, Jacob A.
AU - Wainwright, Ashlea N.
AU - Cawood, Peter A.
N1 - Funding Information:
This work was supported by Australian Research Council grant FL160100168 (NJG, ANW, JAM, and PAC); Leverhulme Trust RPG-2015-422 and EM-2017-047\4 (CJH). This work forms a contribution to the THRIP Project ?Using mineral chemistry to identify base and precious metal mineralization in the Bushveld Complex? at the University of the Witwatersrand. LJR acknowledges the support of the DSI-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis (DSI-NRF CIMERA), at the University of Johannesburg, towards this research. We thank Balz Kamber for editorial handling and useful reviews from two anonymous reviewers.
Funding Information:
This work was supported by Australian Research Council grant FL160100168 (NJG, ANW, JAM, and PAC); Leverhulme Trust RPG-2015-422 and EM-2017-047\4 (CJH). This work forms a contribution to the THRIP Project “Using mineral chemistry to identify base and precious metal mineralization in the Bushveld Complex” at the University of the Witwatersrand . LJR acknowledges the support of the DSI-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis (DSI-NRF CIMERA) , at the University of Johannesburg , towards this research. We thank Balz Kamber for editorial handling and useful reviews from two anonymous reviewers.
Publisher Copyright:
© 2021 Elsevier B.V.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2021/12/20
Y1 - 2021/12/20
N2 - Granite-hosted magmatic-hydrothermal mineral deposits are major sources of Cu, Mo, Sn, Li, and W, originating via mineralizing fluids exsolved from volatile-saturated magmas. We show how trace elements in zircon sampled from the granite-hosted Zaaiplaats tin deposit, Bushveld Complex, preserve a record of both the enrichment of incompatible metals during magma fractionation and those arising from magmatic-hydrothermal mineralization processes. The Zaaiplaats granites are subdivided into three groups; mineralized, altered, and unmineralized. Zircon trace element contents define two trends in a plot of Sn against Gd: Sn/Gd ratios in zircons from the unmineralized samples, as well as the majority of altered samples, define a magma fractionation trend with increasing Y at constant Sn/Gd, whereas those from the mineralized samples are displaced to high Sn/Gd ratios at similar Y. Elevated Sn in the Zaaiplaats zircons is attributed to the introduction of a Sn-rich mineralizing fluid during zircon growth, which occurred at an advanced stage of crystallization (>85%) of the host magma. This model is consistent with the preservation of whole-rock Sn zonation in the Zaaiplaats granites modelled by closed-system magma differentiation and the ensuing exsolution of an acidic, saline Sn-rich magmatic-hydrothermal fluid (Groves and McCarthy, 1978). A metal anomaly, Sn/Sn*, is defined which describes the deviation of Sn over that expected through magma fractionation alone (Sn*), and arises from Sn mobilization due to magmatic-hydrothermal mineralization processes. Identification of metal anomalies such as Sn/Sn* and Cu/Cu* in mineral archives or at the whole-rock level, provides an empirical link to the onset of mineralization processes in magmatic-hydrothermal systems, and can be coupled with geochemical proxies to yield a better understanding of the conditions leading up to, and subsequent to, volatile saturation.
AB - Granite-hosted magmatic-hydrothermal mineral deposits are major sources of Cu, Mo, Sn, Li, and W, originating via mineralizing fluids exsolved from volatile-saturated magmas. We show how trace elements in zircon sampled from the granite-hosted Zaaiplaats tin deposit, Bushveld Complex, preserve a record of both the enrichment of incompatible metals during magma fractionation and those arising from magmatic-hydrothermal mineralization processes. The Zaaiplaats granites are subdivided into three groups; mineralized, altered, and unmineralized. Zircon trace element contents define two trends in a plot of Sn against Gd: Sn/Gd ratios in zircons from the unmineralized samples, as well as the majority of altered samples, define a magma fractionation trend with increasing Y at constant Sn/Gd, whereas those from the mineralized samples are displaced to high Sn/Gd ratios at similar Y. Elevated Sn in the Zaaiplaats zircons is attributed to the introduction of a Sn-rich mineralizing fluid during zircon growth, which occurred at an advanced stage of crystallization (>85%) of the host magma. This model is consistent with the preservation of whole-rock Sn zonation in the Zaaiplaats granites modelled by closed-system magma differentiation and the ensuing exsolution of an acidic, saline Sn-rich magmatic-hydrothermal fluid (Groves and McCarthy, 1978). A metal anomaly, Sn/Sn*, is defined which describes the deviation of Sn over that expected through magma fractionation alone (Sn*), and arises from Sn mobilization due to magmatic-hydrothermal mineralization processes. Identification of metal anomalies such as Sn/Sn* and Cu/Cu* in mineral archives or at the whole-rock level, provides an empirical link to the onset of mineralization processes in magmatic-hydrothermal systems, and can be coupled with geochemical proxies to yield a better understanding of the conditions leading up to, and subsequent to, volatile saturation.
KW - Bushveld complex
KW - Granite hosted mineralization
KW - Hydrothermal fluids
KW - Porphyry pegmatite deposits
KW - Tin tungsten lithium Sn W Li critical metals
KW - Zircon trace elements
UR - http://www.scopus.com/inward/record.url?scp=85117602106&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2021.120580
DO - 10.1016/j.chemgeo.2021.120580
M3 - Article
AN - SCOPUS:85117602106
VL - 585
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 120580
ER -