World-class amethyst-agate geodes from Los Catalanes, Northern Uruguay: genetic implications from fluid inclusions and stable isotopes

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Fiorella Arduin-Rode, Graciela Sosa, Alfons van den Kerkhof, Yves Krüger, David Bajnai, Andreas Pack, Tommaso Di Rocco, Pedro Oyhantçabal, Klaus Wemmer, Daniel Herwartz, Swea Klipsch, Bettina Wiegand, Siegfried Siegesmund, Mathias Hueck
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Abstract

The amethyst and agate geodes from the Los Catalanes Gemmological District in Uruguay represent one of the main deposits of its kind worldwide. The geometry of the deposit is horizontal, with an irregular distribution of amethyst geodes within the upper level of the basalt lava flows and shows strong variations in their abundance, as well as quality, geometry, and shape. Reliable exploration guides are scarce, and the limited knowledge of the geological parameters controlling its occurrence makes exploration unpredictable, leading to inaccurate reserve estimation. Based on cutting-edge methods including nucleation-assisted microthermometry of one-phase fluid inclusions and determination of triple oxygen isotope in silicates and carbonates, as well as analysis of geode-hosted water and groundwater, we estimate the crystallisation temperatures in the range between 15 and 60 °C. These low temperatures point to amethyst crystallisation after the emplacement of the complete basalt pile. The mineralising fluid shows isotopic signatures consistent with meteoric water and very low salinities from pure water up to rarely over 3 wt% NaCl-eq., likely sourced from the groundwater hosted in the aquifers in the basaltic sequence and underlying units. Based on the insights provided by the new data, we propose the combination of open- and closed-system crystallisation inside pre-existing cavities due to the episodic infiltration of meteoric water in a rather stable geological context.

Abstract Image

来自乌拉圭北部洛斯卡塔拉内斯的世界级紫晶-玛瑙晶洞:流体包裹体和稳定同位素的遗传影响
乌拉圭 Los Catalanes 宝石区的紫水晶和玛瑙晶洞是全球同类主要矿藏之一。该矿床的几何形状呈水平状,紫水晶晶洞不规则地分布在玄武岩熔岩流的上层,在数量、质量、几何形状和形状上都有很大的差异。可靠的勘探指南很少,对控制其出现的地质参数的了解有限,使得勘探难以预测,导致储量估计不准确。基于最先进的方法,包括单相流体包裹体的成核辅助显微测温、硅酸盐和碳酸盐中三重氧同位素的测定,以及对地层水和地下水的分析,我们估计其结晶温度在 15 至 60 ° C 之间。这些低温表明紫晶是在完整的玄武岩堆积体形成之后才结晶的。成矿流体显示出与流星水一致的同位素特征,盐度很低,从纯水到很少超过 3 wt% 的 NaCl-eq.,可能来自玄武岩序列和下伏单元含水层中的地下水。根据新数据提供的见解,我们提出了在相当稳定的地质环境中,由于流星水的偶发性渗入,在预先存在的空洞内结合了开放系统和封闭系统结晶的观点。
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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