Abstract The Grasshopper prospect, located 23 km west-southwest from Dillon, Montana, presents exposed zones of phyllic alteration assemblages comprising the early and late phyllic styles. The mineral chemistry of white micas from both phyllic alteration zones was evaluated by short-wave infrared spectroscopy, electron microprobe analysis, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The early phyllic expression consists of white to green micas characterized by longer Al-OH absorption wavelengths (2,204–2,210 nm), whereas the late phyllic phase contains white micas with shorter Al-OH absorption wavelengths (2,197–2,204 nm). Correlation with electron microprobe data found that the Tschermak substitution in the white micas is mainly controlled by Mg concentrations. Based on LA-ICP-MS data, higher Mn and Sr concentrations characterize white micas from the early phyllic alteration, whereas higher concentrations of B, Ba, Cr, Cs, Cu, Li, Rb, Sc, Sn, Ti, Tl, V, and W are present in white micas from the late phyllic style. Systematic zoning patterns of trace element concentrations in white micas from the early and late phyllic alteration styles were confirmed at Grasshopper. In general, increasing trends toward the center of the system were observed in V, Cu, Sc, Sn, W, and Zn, whereas increasing trends outward from the hydrothermal center were reported in Li and Cs. Comparison of the trace element concentrations of white micas from the early phyllic style from the barren system of Grasshopper and the mineralized system of Copper Cliff indicates significant differences in Zn, Cr, B, Tl, Sn, and Cs. Therefore, we propose a preliminary discrimination (Zn + Cr + B vs. Tl + Sn + Cs) plot that can be used to differentiate white micas from the early phyllic alteration among mineralized and weakly to unmineralized systems.

Camilo Uribe-Mogollon

Kierran Maher

Economic Geology

该杂志现为半季刊，由经济地质出版公司 (PUBCO) 于 1905 年首次出版，该公司是一家非营利性公司，旨在出版经济地质学期刊。 1920 年 SEG 成立时，PUBCO 和 SEG 之间的合作安排使该杂志成为该学会的官方机构，PUBCO 同意在封面上的“经济地质学家学会公报”标题下使用该学会的名称”。PUBCO 和 SEG 继续作为合作但独立的实体运营，直到 2001 年 PUBCO 董事会和 SEG 理事会一致同意批准正式的合并协议。PUBCO 董事会以前的活动是现在由出版委员会执行，这是 SEG 内的一个新的自治单位。

Economic Geology is a semi-annual journal first published by the Economic Geology Publishing Company (PUBCO) in 1905. PUBCO is a non-profit organization dedicated to publishing in the field of economic geology. In 1920, with the establishment of SEG, a collaborative arrangement between PUBCO and SEG made Economic Geology the official journal of the society, with PUBCO agreeing to use the title "Bulletin of the Society of Economic Geologists" on the cover. Since then, PUBCO and SEG have operated as collaborative yet independent entities until 2001, when the boards of PUBCO and SEG unanimously agreed to a formal merger. The functions previously held by the PUBCO board are now executed by the new autonomous unit within SEG known as the Publishing Committee.

《Economic Geology》是一本由经济地质出版公司（PUBCO）于1905年首次出版的半季刊。PUBCO是一家非营利性机构，专注于经济地质学领域的出版。1920年，随着SEG的成立，PUBCO与SEG之间建立了合作关系，使《Economic Geology》成为SEG的官方期刊。PUBCO同意在封面上使用“经济地质学家学会公报”的标题。自那时起，PUBCO和SEG作为合作但独立的实体继续运营，直到2001年，PUBCO董事会和SEG理事会一致同意正式合并。PUBCO董事会以前的职能现在由SEG内部的新自治单位——出版委员会执行。

Category	Quartile
地球科学	1
地球科学, 地球化学与地球物理	1
地球科学, 矿物学	1

White Mica Geochemistry: Discriminating Between Barren and Mineralized Porphyry Systems

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