Origin(s) and Significance of Arc-related, Brine-dominated Hydrothermal Alteration, Copiapó Area, Chile

智利科皮亚普地区与电弧相关、以盐水为主的热液蚀变的起源和意义

• 批准号: 0838157
• 负责人: Mark Barton
• 金额: $ 20.95万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838157&HistoricalAwards=false
• 关键词: Origin; Significance; Arc; related; Brine

Fluid flow is a natural and nearly ubiquitous process in the Earth's upper crust. It can fundamentally change the composition of the crust and can create many types of mineral deposits. This project will address the origin of alkali-rich (Na-K-Ca) compositional changes (hydrothermal alteration) that were created by high-temperature circulation of saline fluids. Several complementary approaches will be applied to an exceptionally well exposed area in northern Chile that contains widespread Na-K-Ca-rich alteration and has spatially associated iron oxide-copper-gold-rich ("IOCG") ore deposits. Similar features, though less well exposed, are globally widespread. In spite of the economic importance of IOCG deposits and the likely contribution of alkali-rich alteration to global geochemical cycles, these kinds of hydrothermal systems are poorly documented and their origins are controversial. This project represents a collaboration between academia and the mining industry (Freeport-Moran Copper and Gold) to improve our basic understanding of the fundamental geologic and ore genesis characteristics of these deposits. This new project will test the hypotheses: (1) that large portions of the shallow crust are altered to alkali-rich compositions as a result of the circulation of brines, (2) that those brines derive from sedimentary or surficial sources and not from crystallizing hydrous magmas, and (3) that there is a genetic link between this style of alteration and the IOCG family of deposits. The work will begin with geologic mapping of alteration across the Mesozoic magmatic arc of northern Chile to establish the volumes, distribution, and relative timing of hydrothermal features. If of external origin, these features should be controlled by regional structures and stratigraphy rather than by an association with particular igneous rocks (e.g., those that formed from magmas with high water contents and are typically associated with other distinctive types of ore-forming systems, notably the "porphyry copper" family). Geochemical analyses to determine whole rock and isotopic (H, B, C, O, S, Sr) compositions, petrologic studies of mineral assemblages, and U-Pb geochronology will supplement the field work by providing key documentation of: (a) the extent of compositional changes, (b) the source of fluids and dissolved components, (c) the depth, temperature, and chemical conditions of alteration, and (d) the absolute timing and correlation of magmatic events and hydrothermal features. From the anticipated results combined with related work it should be possible to assess better the types, extents, and origins of Na-Ca-K hydrothermal alteration and the consequences for material fluxes in brine-dominated hydrothermal systems at scales from individual intrusives centers to global arc magmatism. Inferences regarding system-scale processes will be fundamental to building better deposit-scale models useful in mineral exploration for IOCG deposits, and should help distinguish these systems from the economically more productive porphyry Cu-Mo-Au environment. This project will support two graduate students, it will complement the PhD project of another who is supported by industry, and it will engage in the research two continuing undergraduate geology students. Two of these students are women and two belong to minority groups. Materials will be archived in collections at the University of Arizona; these collections are heavily used for continuing education courses for professionals, for regular courses and for topical studies.

流体流动是地球上地壳中一种自然且几乎普遍存在的过程。它可以从根本上改变地壳的成分，并可以形成多种类型的矿藏。该项目将解决由盐水流体的高温循环引起的富碱（Na-K​​-Ca）成分变化（热液蚀变）的起源。几种补充方法将应用于智利北部一个异常暴露的地区，该地区包含广泛的富含Na-K-Ca的蚀变，并且具有空间相关的富含氧化铁-铜-金（“IOCG”）矿床。类似的特征虽然不太明显，但在全球范围内普遍存在。尽管IOCG矿床具有重要的经济意义，而且富碱蚀变可能对全球地球化学循环做出贡献，但这类热液系统的记录很少，而且它们的起源也存在争议。该项目代表了学术界和采矿业（自由港莫兰铜金矿）之间的合作，以提高我们对这些矿床的基本地质和成矿特征的基本了解。 这个新项目将测试以下假设：(1) 由于盐水循环，大部分浅地壳被蚀变成富含碱的成分，(2) 这些盐水来自沉积物或地表来源，而不是来自结晶的含水岩浆，(3) 这种蚀变类型与 IOCG 沉积物家族之间存在遗传联系。这项工作将从绘制智利北部中生代岩浆弧蚀变地质图开始，以确定热液特征的体积、分布和相对时间。如果是外部成因，这些特征应受区域结构和地层学控制，而不是与特定火成岩相关（例如，由高含水量岩浆形成的岩浆，通常与其他独特类型的成矿系统相关，特别是“斑岩铜”族）。确定整个岩石和同位素（H、B、C、O、S、Sr）成分的地球化学分析、矿物组合的岩石学研究和 U-Pb 地质年代学将通过提供以下关键文件来补充现场工作：（a）成分变化的程度，（b）流体和溶解成分的来源，（c）蚀变的深度、温度和化学条件，以及（d） 岩浆事件和热液特征的绝对时间和相关性。根据预期结果与相关工作相结合，应该可以更好地评估 Na-Ca-K 热液蚀变的类型、范围和起源，以及从单个侵入中心到全球弧岩浆作用范围内以盐水为主的热液系统中物质通量的后果。关于系统规模过程的推论对于建立更好的矿床规模模型至关重要，可用于 IOCG 矿床的矿物勘探，并且应有助于将这些系统与经济上更具生产力的斑岩铜-钼-金环境区分开来。该项目将支持两名研究生，它将补充另一个由工业界支持的博士项目，并将从事两名继续本科地质学学生的研究。其中两名学生是女性，两名学生属于少数群体。材料将被存档在亚利桑那大学的馆藏中；这些馆藏大量用于专业人员的继续教育课程、常规课程和专题研究。