资源勘查工程毕业设计（论文）外文译文- 岩浆岩热矽卡岩型矿床中成矿流体的组成和演化.doc

成 都 理 工 大 学学生毕业设计（论文）外文译文学生姓名：马福学号：200601050315专业名称：资源勘查工程译文标题（中英文）：composition and evolution of ore fluids in a magmatic-hydrothermal skarn deposit 岩浆岩热矽卡岩型矿床中成矿流体的组成和演化译文出处：geology指导教师审阅签名： 外文译文正文：摘要通过对墨西哥伸斯麦矽卡岩型矿床卤水的化学成分，蒸汽，低盐度流体包裹体质子激发x荧光分析，没有证据表明外部流体投入符合不断变化的岩浆热液系统。研究结果支持一个在高温和岩石静压力下调用早期相分的岩浆流体进入卤水和蒸汽(两相场)其次是在较低温度和静水压力下包封低盐度岩浆流体 (一相场)的模型。早期的卤水和蒸汽夹杂含有高浓度的铅，锌和低浓度铜;但是蒸汽比盐水包含吏多的铜，并有可能作为一种硫的络合物来运输。对铜流体相变行为的观察是和斑岩铜矿系统相娘美的。后来，仰斯麦矿床的低矿化度流体描述了高krca值岩浆流体的不同脉冲其中基本金属，包括铜，被氯化物络合物运移。由铜，铅，锌的共生关系和相对浓度的变化认为，这种流体是形成矿床的主要原因。斯麦矿床流体包裹体中铜，铅，锌的富集与整个墨西哥的高温碳酸盐矿床的基本金属矿石测量结果相一致，并认为这些矿床中大部分金属元素的供应主要是受岩浆热液中铜元素的不足所控制。引言金属矿床产出在斑岩侵入到碳酸盐岩的构造或其周围是世界上斑岩型、矽卡岩型、管状和席状类型是cu、pb、zn、ag和au矿床的主要来源，这反映出了从近端到远端的侵入(后三种类型总称为高温碳酸盐交代矿床)。对矽卡岩型和斑岩型矿床的流体包裹体的评价证明它们形成的临界因素食来源于长英质岩浆的含金属矿物流体的出溶(burnham,1979;kwak,1986;bodnar,1995;hedenquist等人.1998;meinert等人，1997，2003;kamenetsky等人，1999,2002;fulignti等人，200l;baker和lang,2003)。通常来说，早期溶解出的流体以不混容的卤水和蒸气形式存在(两相场;burnham,1979;bodnar,l995)，但是，后来由于温度压力的变化，早期的脱气和热量损耗使流体流量降低(shinohara和hedenquist,1997)，导致了再一相场下低盐度岩浆流体的捕获(hedenquist等人，1998；menier等人，1997,2003；baker和lang,2003;图1)。一些微量分析技术的进步，比如激光电感模式结合大量等离子体光谱测定(la-icp-ms;audetat等人,1992;ulrich等人,1999,2002)技术产生了对斑岩型矿床中卤水和蒸汽包体的化学物质直接分析的壮观结果(如heinrich等人,1999;ulrich等人,1999,2002)。卡岩矿床补充数据的存在，而且一直没有低盐度流体和矿床类型的微量化学评价了解后期流体的化学性质是至关重要的，因为在是否已岩浆流体为主(harris和kesler,2002;meinert等人,2003)或是来自外部的流体侵入(reynolds和beane,1985;haynes和kesler,1988;taylor,1992)上存在太多争议。在本文中，论述了对墨西哥卑斯麦矽卡岩矿床早期岩浆卤水蒸汽包体和低盐流体包裹体总体的质子激发x荧光分析。结果显示矽卡岩矿床中卤水蒸气包体之间的金属划分的最初认识和强调在金属沉积中低盐度流体的重要性。此外，数据表明了对岩浆热液流体为基地的金属浓聚无核大量矿石之间关系的认识，属于墨西哥的crds。正开采的墨西哥卑斯麦矿床与岩株接触的矽卡岩有关的块状硫化物中含有锌、铅、铜、银矿。bakerandlang曾介绍过地质概况和超群流体包裹体历史(2003)。矿化作用的空间和短暂的与自提纪碳酸盐岩中放置的第三纪黑云母石英二长斑岩岩株有关。岩株和矿石的侵位都受仰斯麦断层的控制，在断层的下盘内，外部矽卡岩石榴石同向且呈近乎垂直的岩席。硫化物主要矿化阶段是接在矽卡岩之后，是由闪锌矿，方铅矿，黄铁矿，磁黄铁矿和黄铜矿组成的。最早的流体包裹体是在成矿之前的萤石和石英内产生的，它与最初的卤水和蒸汽夹杂物共存。大多数最初的卤水夹杂在均一的温度范围内(400至goo。c)，含盐量估计等量于浓度为32到62nacl溶液中盐的含量。由于典型的均化现象难以观测，所以目前还没有蒸气包体的数据记录。压力的估计表明圈闭压力在不混容性期间约为450巴。从成旷之前到共同成矿的石英中主要的夹杂物含有 40-60蒸气，在 351-438。c，25obar的条件下呈现出临界或近于临界的均化状态。盐度估计等量于浓度为84到 10.nacl溶液中盐的含量。富矿流体(蒸汽含量占总体积的10-40)从共同成矿到成矿之后的总体，包括首次到二次夹杂在共同成矿的萤石，均化温度的石英和盐度 (104-33c)估计等量于浓度为32到62nacl溶液中盐的含量。事实上，这些夹杂物局部在140巴的压力沸腾的情况下与富矿蒸汽夹杂物共存。bakel、和lang (2003)提出了岩浆热液矽卡岩系统的初始条件较高的温度 (约50o。c)，从而导致了成矿之前的岩浆流体在两相场(不相溶的盐水和蒸汽夹杂物)情况下的俘获。由于傅斯麦断层的向前运动大大改变了温度压力条件，这也导致了主要压力从静岩压力下降到流体静压力(约140巴)，温度从500。c下降到小于350。c。在低盐度、一相场的岩浆流体 (临界包体)情况下捕获了流体包裹体。流体进一步发展产生了同步形成矿石，成矿后的矿石和富矿液体包体。卤水、蒸气、低报h蔓流体包裹体的质子激发x荧光分析在澳大利亚北赖德英联邦科学和工业研究组织(cslr)用核微探针进行了质子激发x荧光分析。ryan等人(2001)对技术的细节做了报告。表1总结了盐水，蒸汽，临界点和富矿液体石英包裹体的变化范围(最大值和最小值 )和平均组成。质子激发x荧光方法的成像能力提供7在流体包裹体内元素分布的详细计算(图2)。正如预料的那样，氯元素的浓度在卤水包裹体中最高，并包含在固相之间有着明显的优势;高频分量与钾盐(kcl)和石盐(由于na原子量太轻而不能做质子激发 x荧光分析)相关联。钙、锰、铁在液相和日前尚未确认的固相内部有出现。围绕若汽泡的液相含有大量富矿蒸气和临界包体的溶质。在离析的时候，局部的富矿蒸气包裹体和固相会被重要的液体配合剂所捕获(如混合的蒸气卤水包裹体)。铅锌的最高浓度出现在早期卤水和蒸汽包裹体内0)3000 pm) ;后来金属浓度会出现明显的下降f成低盐度的包裹休。总的来说和钳锌相比铜浓度在所有包体类型中是比较低的(700pm)。和铅锌不同，铜在卤水包体中有最低的浓度，而在蒸气包体中有着最高的浓度。临界包体往往记录着比卤水包体更高的铜浓度；较少部分的铜产生在晚期的富矿流体包裹体内。图2 质子激发x荧光分析图a- 卤水；b-蒸汽；c-临界包体结 论对仲斯麦矽卡岩矿床中的卤水，蒸气，低盐度流体包裹体的质子激发x荧光分析，认为三种流体类型都为岩浆成因。在早期的卤水和蒸气包体中铅锌的浓度最高，除此以外，矿石建造很可能是低盐度岩浆流动产生的。铜元素浓度明显低于铅锌浓度，但在早期的蒸气包体中含量最高，其中包体中硫元素复合物有可能非常重要。然而，氯化物是后期低盐度岩浆流体的情况下形成铜元素运移的原因。数据表明，矽卡岩矿床的流体演化和一些斑岩系统的流体演化过程相似，两种矿床类型中岩浆热液流体控制着大量金属元素的富集。表1 卑斯麦矿床卤水、蒸汽、临界和富矿流体包裹体pixe分析卤水（n=9）蒸汽（n=15）临界(n=10)富矿流体(n=5)平均值最大值最小值平均值最大值.最小值平均值最大值最小值平均值最大值最小值cl (wt%)28.9345.806.181.622.840.443.119.470.484.9013.891.38k (wt%)6.0610.680.071.071.060.17ca (wt%)3.706.021.540.902.680.190.300.710.090.270.470.07mn (wt%)0.812.110.060.120.400.020.030.140.010.010.030.01fe (wt%)0.650.580.040.060.160.010.050.110.01cu (ppm)9414742395694143193474567620834zn (ppm)31347214438799215521645416054615533832pb (ppm)33559478691246555262277281547332466926257as (ppm)43616131284401029186842594211025538br (ppm)7742042839262496192386886206268530155k/ca1.682.920.901.574.650.053.608.100.793.217.600.92zn/pb0.961.390.510.411.300.110.601.330.100.320.520.12zn/cu38.7080.619.522.789.960.402.736.590.442.334.250.94composition and evolution of ore fluids in a magmatic-hydrothermal skarn depositabstractthe chemistry of brine, vapor, and low-salinity fluid inclusions measured by proton-induced x-ray emission from the bismark skarn deposit, mexico, is consistent with an evolving magmatic- hydrothermal system with no evidence for external fluid inputs. the results support a model that invokes early phase separation of magmatic fluids into brine and vapor (two-phase field) at high temperature and lithostatic pressure, followed by the entrapment of a low-salinity magmatic fluid (one-phase field) at lower temper- ature and hydrostatic pressure. the early brine and vapor inclu- sions contain high pb and zn concentrations and low cu; however, the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex. the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems. the later, low-salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k/ca ratio in which base metals, including cu, were transported by chloride complexes. paragenetic relationships and variations in the relative concentra- tions of cu, pb, and zn suggest that this fluid was primarily re- sponsible for ore deposition. the relative cu, pb, and zn concen- trations in fluid inclusions at bismark are consistent with those measured from base-metal ores in high-temperature carbonate- replacement deposits throughout mexico, and suggest that the bulk-metal budget of these deposits is primarily controlled by magmatic-hydrothermal fluids deficient in cu.introductionore deposits hosted in and around porphyritic intrusions emplaced into carbonate rocks constitute a major source of the worlds cu, pb, zn, ag, and au. deposit types range from porphyry to skarn to chimney and manto styles (the latter three collectively called high- temperature carbonate-replacement deposits crds) that reflect prox- imal to distal settings from intrusions (einaudi et al., 1981; megaw et al., 1988; titley, 1993). evaluation of fluid inclusions in skarn and porphyry deposits has shown that a critical factor in their formation is the exsolution of metal-bearing fluids from felsic magmas (burnham,1979; kwak, 1986; bodnar, 1995; hedenquist et al., 1998; meinert et al., 1997, 2003; kamenetsky et al., 1999, 2002; fulignati et al., 2001; baker and lang, 2003). commonly the earliest-exsolved fluids occur as immiscible brine and vapor (two-phase field; burnham, 1979; bod- nar, 1995), but subsequent changes in pressure and temperature (p-t) conditions due to lower fluid flux as a result of early degassing and heat loss (shinohara and hedenquist, 1997) can result in entrapment of a late, low-salinity magmatic fluid in the one-phase field (hedenquist et al., 1998; meinert et al., 1997, 2003; baker and lang, 2003; fig.1). advances in microanalytical techniques such as the laser ablationinductively coupled plasmamass spectrometry (la-icp-ms; audetat et al., 1998; heinrich et al., 1999; ulrich et al., 1999, 2002) and proton- induced x-ray emission (pixe; heinrich et al., 1992; ryan et al., 2001,1993; kamenetsky et al., 2002) techniques have led to the direct anal- ysis of the chemistry of brine and vapor inclusions in porphyry de- posits with spectacular results (e.g., heinrich et al., 1999; ulrich et al.,1999, 2002). unfortunately, no complementary data exist for skarn deposits, and furthermore there has been no microchemical evaluation of the later, low-salinity fluids in either deposit type. understanding the chemistry of the later fluids is critical because there is much con- troversy as to whether they are dominantly magmatic fluids (harris and golding, 2002; meinert et al., 2003) or derived from fluids external to the intrusions (reynolds and beane, 1985; haynes and kesler, 1988; taylor, 1992).in this paper we report pixe analyses of early magmatic brine and vapor inclusions, and a population of later, low-salinity fluid in- clusions from the bismark skarn deposit, mexico. the results provide the first insights into metal partitioning between brine and vapor in- clusions in skarn deposits, and also highlight the importance of low- salinity magmatic fluids in ore deposition. furthermore, the data pro-vide insights into the relationship between magmatic-hydrothermal fluid base-metal concentrations and bulk-ore grades in mexican crds.geology and fluid evolution of the bismark skarnthe operating bismark mine, mexico, contains zn, pb, cu, and ag ore in massive sulfide associated with stock-contact skarn (8.5 mt at 8% zn, 0.5% pb, 0.2% cu, and 50 g/t ag; haptonstall, 1994). the geology and complex fluid-inclusion history were described by baker and lang (2003). mineralization is spatially and temporally related to a tertiary biotite quartz monzonite porphyry stock emplaced into cre- taceous carbonate rocks. emplacement of both the stock and ore was controlled by the bismark fault, and massive prograde garnet exoskarn forms a nearly vertical sheet mostly within the footwall to the fault. main-stage sulfide mineralization postdates prograde skarn and com- prises sphalerite, galena, pyrite, pyrrhotite, and chalcopyrite. the ear- liest fluid inclusions occur within pre-ore fluorite and quartz, and are coexisting primary brine and vapor inclusions. the majority of primary brine inclusions have homogenization temperatures ranging from 400 to 600 c and salinity estimates range between 32 and 62 wt% nacl equivalent. no data were recorded for vapor inclusions because of the typical difficulty of observing homogenization phenomena. pressure estimates suggest entrapment pressures of 4450 bar during immisci- bility. primary inclusions in pre-ore to syn-ore quartz contain 4060 vol% vapor and exhibit critical to near-critical homogenization behav- ior between 351 and 438 c at pressures of 4250 bar. salinity estimates range from 8.4 to 10.9 wt% nacl equivalent. a population of syn-ore to post-ore, liquid-rich (1040 vol% vapor) inclusions that occur as primary to secondary inclusions in syn-ore fluorite and quartz have homogenization temperatures and salinities that range from 104 to 336c and from 5.1 to 11.8 wt% nacl equivalent. the fact that these inclusions locally coexist with vapor-rich inclusions indicates that boil- ing occurred at pressures of 4140 bar.figure 1. pressure vs. temperature plot for nacl-h2o system, illus- trating entrapment of bismark fluid inclusions in two-phase and one- phase field and average base-metal concentrations in brine, vapor, and critical inclusions.baker and lang (2003) suggested that the initial conditions for the magmatic-hydrothermal skarn system were high temperature (4500c) and lithostatic pressure (4450 bar; fig. 1), resulting in the entrap- ment of pre-ore magmatic fluids in the two-phase field (immiscible brine and vapor inclusions). the p-t conditions were then significantly modified due to movement along the bismark fault. this resulted in a major pressure drop from lithostatic to hydrostatic pressure (4140 bar), and subsequent cooling from 4500 c to 350 c (fig. 1). fluid inclusions trapped during this event contain a low-salinity, one-phase field magmatic fluid (critical inclusions); their trapping coincided with the onset of the main ore stage. the fluid evolved further to produce the syn-ore to post-ore, liquid-rich inclusions.pixe analyses of brine, vapor, and low-salinity fluid inclusionspixe analysis was carried out on the commonwealth scientific and industrial research organisation (csiro) nuclear microprobe, north ryde, australia. details of the technique were reported in ryan et al. (2001, and references therein). table 1 summarizes the range (maximum and minimum values) and mean composition for the brine, vapor, critical, and liquid-rich inclusions in quartz. the imaging ca- pacity of the pixe method allows a detailed evaluation of the distri- bution of elements within the fluid inclusions (figs. 2a, 2b, and 2c).figure 2. proton-induced x-ray emission images of (a) brine, (b) vapor, and (c) critical inclusions. zones of high concentration of particular element coincide with red, yellow to white colors (in in- creasing abundance) and blue to black represent low to zero con- centration, respectively. numerical concentration in each picture is bulk element concentration in fluid inclusion.conclusionspixe analyses from brine, vapor, and low-salinity fluid inclusions in the bismark skarn deposit are consistent with a magmatic origin for all three fluid types. pb and zn concentrations are highest in the early brine and vapor inclusions, but ore formation likely occurred from the low-salinity magmatic fluid. cu concentrations are significantly lower than pb and zn, but are highest in the early vapor inclusions where s complexes were likely important. however, chloride was responsible for cu transport in the late, low-salinity magmatic fluid. the data suggest that the fluid evolution of skarn deposits is similar to the fluid evolution of some porphyry systems and that the magmatic- hydrothermal fluid controls the bulk-metal budget of both deposit types.table 1. pixe analysis of brine, vapor, critical, and liquid-rich inclusions from the bismark depositbrine (n = 9)vapor (n = 15)）critical (n = 10)liquid-rich (n = 5)meanmax.min.meanma