High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico
High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico
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DOI：
10.2113/gsecongeo.83.8.1856
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发表时间：
1988-12
期刊：
影响因子：
5.8
通讯作者：
P. Megaw;J. Ruíz;S. Titley
中科院分区：
文献类型：
--
作者：
P. Megaw;J. Ruíz;S. Titley
墨西哥北部以碳酸盐为主的高温银铅锌(铜)矿床赋存于以碳酸盐为主的侏罗纪-白垩纪盆地沉积序列中，沉积层序被古生代或更古老的地壳所淹没。这些地区位于一个主要的褶皱冲断带内或边缘；与该带走向平行的构造控制着许多地区的矿化。除三个地区外，所有地区都发现了第三纪时代的蚀变和/或矿化的火山岩和侵入岩；矿化显然发生在47至26英里的受限时期。过去，矿床的特征是不规则的矿透镜，通常揭示出强烈的构造控制，并且在地层上是不一致的。矿体有三种主要形态类型：地幔、烟囱和豆荚，由块状硫化物和(或)钙硅酸盐夕卡岩组成。硫化物螳螂和烟囱被包裹在碳酸盐岩中，通常远离侵入体。硫化物螳螂通常向下进入硫化物烟囱，后者又可能向下进入以岩脉为核心的夕卡岩烟囱。豆荚状夕卡岩和硫化物矿体主要沿岩屑、岩脉或岩床接触产出，但它们也可能在距离侵入性接触一定距离处发育。尽管矿石类型不同，但在构造控制、寄主岩石特征和硫化物矿物学方面存在着主要的相似之处。构造控制包括侵入接触、断层、褶皱轴线、裂缝、裂隙和洞穴带。夕卡岩中最重要的是侵入接触和与侵入有关的断层，而区域断层、褶皱和断裂系统是对螳螂和烟囱的主要控制。矿化通常发生在相对不透水的页岩单元、岩床或火山岩之下，但一些广泛的矿体在表面上均质的碳酸盐岩序列中表现出对特定层位的显著限制。对矿化和未矿化地层的研究发现，矿石沉积与碳酸盐成分、相、有机含量或不溶成分之间没有一致的联系。然而，重结晶、加热、变形或热液白云岩作用引起的次生孔隙度和渗透率增强带是重要的成矿控制因素。矿床的地球化学数据很少，但显示出一些主要地区的强烈对比条件。流体包裹体数据显示，温度在200摄氏度到500摄氏度之间，盐度在I到60当量重量百分比的氯化钠之间。温度较高、盐度较高的溶液通常来自矽卡岩带。沸腾的证据还没有报道。Naica、Concepcion del Oro和Velardefia的夕卡岩矿石的硫化物硫同位素值接近0，而Santa Eulalia的夕卡岩和块状硫化物矿石的硫化物同位素值范围很大。在大多数情况下，方铅矿和闪锌矿、磁黄铁矿或黄铁矿之间存在同位素不平衡。矿化上方的方解石细脉网络和矿化附近的石灰岩围岩显示碳、氧同位素向较轻的值移动。紧密聚集的硫同位素和高温、高盐度流体包裹体被解释为Naica、Concepcion del Oro和Velardena成矿流体中有强烈的岩浆成分，但Santa Eulalia和其他地区的证据表明岩浆流体和大气流体之间存在广泛的混合。这些矿床所显示的成矿类型光谱似乎代表了对侵入体组合、侵位深度、容矿岩石特征和个别系统的地球化学演化的不同响应。
The high-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico occur in thick carbonate-dominant Jurassic-Cretaceous basinal sedimentary sequences floored by Paleozoic or older crust. The districts lie within, or on the margins of, a major fold-thrust zone; structures parallel to the trends of this belt control mineralization in many districts. Altered and/or mineralized volcanic and intrusive rocks of Tertiary age are found in all but three of the districts; mineralization apparently occurred during a restricted period 47 to 26 m.y. ago.The deposits are characterized by irregular ore lenses that commonly reveal strong structural controls and are stratigraphically discordant. Orebodies are of three principal morphological types: mantos, chimneys, and pods and are composed of massive sulfides and/or calc-silicate skarn. Sulfide mantos and chimneys are enclosed within carbonate rocks and are generally remote from intrusive bodies. Sulfide mantos commonly grade downward into sulfide chimneys, which may in turn grade downward into skarn chimneys cored by dikes. Podiform skarn and sulfide orebodies principally occur along stock, dike, or sill contacts, but they may also be developed at some distance from an intrusive contact. The associated intrusions are not widely mineralized.Despite the variations between ore types, major similarities are seen in structural controls, host-rock characteristics, and sulfide mineralogy. Structural controls include intrusive contacts, faults, fold axes, fractures, fissures, and cavern zones. Intrusive contacts and intrusion-related faults are most important in the skarns, whereas regional fault, fold, and fracture systems are dominant controls on mantos and chimneys. Mineralization commonly occurs below relatively impermeable shaly units, sills or volcanic rocks, but some extensive orebodies show remarkable restriction to specific horizons within apparently homogeneous carbonate successions. Studies of mineralized and unmineralized strata have found no consistent links between ore deposition and carbonate composition, facies, organic content, or insoluble components. However, zones of secondarily enhanced porosity and permeability induced by recrystallization, heating, deformation, or hydrothermal dolomitization are important mineralization controls.Geochemical data for the deposits are sparse but indicate strongly contrasting conditions among some of the major districts. Fluid inclusion data indicate temperatures in the range 200 degrees to 500 degrees C and salinities ranging from i to 60 equiv wt percent NaCl. The hotter, more saline, solutions are typically from skarn zones. Evidence for boiling has not been reported. The skarn ores of Naica, Concepcion del Oro, and Velardefia show tight clustering of sulfide sulfur isotope values near 0, whereas the skarn and massive sulfide ores of Santa Eulalia show a wide range of values. In most cases there is isotopic disequilibrium between galena and sphalerite, pyrrhotite, or pyrite. Calcite veinlet stockworks above mineralization and limestone wall rocks adjacent to mineralization show shifts of carbon and oxygen isotopes to lighter values. The tightly clustered sulfur isotopes and high-temperature, high-salinity fluid inclusions have been interpreted as indicating a strong magmatic component in the mineralizing fluids at Naica, Concepcion del Oro, and Velardena, but Santa Eulalia and other districts show evidence suggesting extensive mixing between magmatic and meteoric fluids.It appears that the spectrum of mineralization styles shown by these deposits represent differing responses to variations in intrusive associations, depth of emplacement, host-rock characteristics, and geochemical evolution of the individual systems.