{"title":"Formation of Topaz-Greisen by a Boiling Fluid: A Case Study from the Sn-W-Li Deposit, Zinnwald/Cínovec","authors":"Shilei Qiao, Timm John, A. Loges","doi":"10.5382/econgeo.5074","DOIUrl":null,"url":null,"abstract":"\n Zinnwald/Cínovec is one of the largest Li-Sn-W greisen deposits in Europe. Greisens in general are important hosts for many major ore deposits of several high-tech elements—most prominently Sn, W, and Li. However, the mechanisms of greisenization in relationship to ore formation are still not well understood, especially for the important case of fluoride-rich greisen. Here, we investigate the sequence and formation mechanism of the topaz-greisen in the Zinnwald/Cínovec deposit. Based on the mineral abundances, the alteration profile can be divided into four distinct zones: (1) rhyolite, (2) albitite, (3) low-degree greisen, and (4) high-degree greisen. In the greisen zones, almost all the feldspar has been replaced by topaz (up to 12 vol %) + quartz (up to 78 vol %), and the abundance of mica gradually decreases from 11 to 3 vol % with increasing degree of greisenization. Mass balance calculations indicate a net influx of F and silica during greisenization.\n Our observations are best explained by a two-stage greisenization process involving phase separation by boiling in the pore space of the sample: first an acidic HF-rich phase, likely a vapor, reacted with feldspar to form topaz and quartz in a dissolution-precipitation reaction. This reaction created substantial transient porosity, which was subsequently sealed by the precipitation of quartz and fluorite from a boiling liquid. We interpret the vapor and liquid as emerging from a common supercritical aqueous parental fluid. The characteristic sequence of creation of pore space by a vapor and the subsequent reduction of porosity by precipitation from the associated boiling liquid constrain the conditions and time available for ore formation. This study evaluates the mechanism of topaz greisenization and the controls on porosity evolution, which are crucial to ore element redistribution.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.5000,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Economic Geology","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.5382/econgeo.5074","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Zinnwald/Cínovec is one of the largest Li-Sn-W greisen deposits in Europe. Greisens in general are important hosts for many major ore deposits of several high-tech elements—most prominently Sn, W, and Li. However, the mechanisms of greisenization in relationship to ore formation are still not well understood, especially for the important case of fluoride-rich greisen. Here, we investigate the sequence and formation mechanism of the topaz-greisen in the Zinnwald/Cínovec deposit. Based on the mineral abundances, the alteration profile can be divided into four distinct zones: (1) rhyolite, (2) albitite, (3) low-degree greisen, and (4) high-degree greisen. In the greisen zones, almost all the feldspar has been replaced by topaz (up to 12 vol %) + quartz (up to 78 vol %), and the abundance of mica gradually decreases from 11 to 3 vol % with increasing degree of greisenization. Mass balance calculations indicate a net influx of F and silica during greisenization.
Our observations are best explained by a two-stage greisenization process involving phase separation by boiling in the pore space of the sample: first an acidic HF-rich phase, likely a vapor, reacted with feldspar to form topaz and quartz in a dissolution-precipitation reaction. This reaction created substantial transient porosity, which was subsequently sealed by the precipitation of quartz and fluorite from a boiling liquid. We interpret the vapor and liquid as emerging from a common supercritical aqueous parental fluid. The characteristic sequence of creation of pore space by a vapor and the subsequent reduction of porosity by precipitation from the associated boiling liquid constrain the conditions and time available for ore formation. This study evaluates the mechanism of topaz greisenization and the controls on porosity evolution, which are crucial to ore element redistribution.
期刊介绍:
The journal, now published semi-quarterly, was first published in 1905 by the Economic Geology Publishing Company (PUBCO), a not-for-profit company established for the purpose of publishing a periodical devoted to economic geology. On the founding of SEG in 1920, a cooperative arrangement between PUBCO and SEG made the journal the official organ of the Society, and PUBCO agreed to carry the Society''s name on the front cover under the heading "Bulletin of the Society of Economic Geologists". PUBCO and SEG continued to operate as cooperating but separate entities until 2001, when the Board of Directors of PUBCO and the Council of SEG, by unanimous consent, approved a formal agreement of merger. The former activities of the PUBCO Board of Directors are now carried out by a Publications Board, a new self-governing unit within SEG.