資源勘查工程畢業(yè)設計（論文）外文譯文 巖漿巖熱矽卡巖型礦床中成礦流體的組成和演化

1、成 都 理 工 大 學學生畢業(yè)設計（論文）外文譯文學生姓名：馬福學號：200601050315專業(yè)名稱：資源勘查工程譯文標題（中英文）：composition and evolution of ore fluids in a magmatic-hydrothermal skarn deposit 巖漿巖熱矽卡巖型礦床中成礦流體的組成和演化譯文出處：geology指導教師審閱簽名： 外文譯文正文：摘要通過對墨西哥伸斯麥矽卡巖型礦床鹵水的化學成分，蒸汽，低鹽度流體包裹體質子激發(fā)x熒光分析，沒有證據表明外部流體投入符合不斷變化的巖漿熱液系統(tǒng)。研究結果支持一個在高溫和巖石靜壓力下調用早期相分的巖漿流體

2、進入鹵水和蒸汽(兩相場)其次是在較低溫度和靜水壓力下包封低鹽度巖漿流體 (一相場)的模型。早期的鹵水和蒸汽夾雜含有高濃度的鉛，鋅和低濃度銅;但是蒸汽比鹽水包含吏多的銅，并有可能作為一種硫的絡合物來運輸。對銅流體相變行為的觀察是和斑巖銅礦系統(tǒng)相娘美的。后來，仰斯麥礦床的低礦化度流體描述了高krca值巖漿流體的不同脈沖其中基本金屬，包括銅，被氯化物絡合物運移。由銅，鉛，鋅的共生關系和相對濃度的變化認為，這種流體是形成礦床的主要原因。斯麥礦床流體包裹體中銅，鉛，鋅的富集與整個墨西哥的高溫碳酸鹽礦床的基本金屬礦石測量結果相一致，并認為這些礦床中大部分金屬元素的供應主要是受巖漿熱液中銅元素的不足所控制。

3、引言金屬礦床產出在斑巖侵入到碳酸鹽巖的構造或其周圍是世界上斑巖型、矽卡巖型、管狀和席狀類型是cu、pb、zn、ag和au礦床的主要來源，這反映出了從近端到遠端的侵入(后三種類型總稱為高溫碳酸鹽交代礦床)。對矽卡巖型和斑巖型礦床的流體包裹體的評價證明它們形成的臨界因素食來源于長英質巖漿的含金屬礦物流體的出溶(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)。通常來說，早期溶解出的流體以不混容

4、的鹵水和蒸氣形式存在(兩相場;burnham,1979;bodnar,l995)，但是，后來由于溫度壓力的變化，早期的脫氣和熱量損耗使流體流量降低(shinohara和hedenquist,1997)，導致了再一相場下低鹽度巖漿流體的捕獲(hedenquist等人，1998；menier等人，1997,2003；baker和lang,2003;圖1)。一些微量分析技術的進步，比如激光電感模式結合大量等離子體光譜測定(la-icp-ms;audetat等人,1992;ulrich等人,1999,2002)技術產生了對斑巖型礦床中鹵水和蒸汽包體的化學物質直接分析的壯觀結果(如heinrich等人,

5、1999;ulrich等人,1999,2002)。卡巖礦床補充數據的存在，而且一直沒有低鹽度流體和礦床類型的微量化學評價了解后期流體的化學性質是至關重要的，因為在是否已巖漿流體為主(harris和kesler,2002;meinert等人,2003)或是來自外部的流體侵入(reynolds和beane,1985;haynes和kesler,1988;taylor,1992)上存在太多爭議。在本文中，論述了對墨西哥卑斯麥矽卡巖礦床早期巖漿鹵水蒸汽包體和低鹽流體包裹體總體的質子激發(fā)x熒光分析。結果顯示矽卡巖礦床中鹵水蒸氣包體之間的金屬劃分的最初認識和強調在金屬沉積中低鹽度流體的重要性。此外，數據表

6、明了對巖漿熱液流體為基地的金屬濃聚無核大量礦石之間關系的認識，屬于墨西哥的crds。正開采的墨西哥卑斯麥礦床與巖株接觸的矽卡巖有關的塊狀硫化物中含有鋅、鉛、銅、銀礦。bakerandlang曾介紹過地質概況和超群流體包裹體歷史(2003)。礦化作用的空間和短暫的與自提紀碳酸鹽巖中放置的第三紀黑云母石英二長斑巖巖株有關。巖株和礦石的侵位都受仰斯麥斷層的控制，在斷層的下盤內，外部矽卡巖石榴石同向且呈近乎垂直的巖席。硫化物主要礦化階段是接在矽卡巖之后，是由閃鋅礦，方鉛礦，黃鐵礦，磁黃鐵礦和黃銅礦組成的。最早的流體包裹體是在成礦之前的螢石和石英內產生的，它與最初的鹵水和蒸汽夾雜物共存。大多數最初的鹵水

7、夾雜在均一的溫度范圍內(400至goo。c)，含鹽量估計等量于濃度為32到62nacl溶液中鹽的含量。由于典型的均化現象難以觀測，所以目前還沒有蒸氣包體的數據記錄。壓力的估計表明圈閉壓力在不混容性期間約為450巴。從成曠之前到共同成礦的石英中主要的夾雜物含有 40-60蒸氣，在 351-438。c，25obar的條件下呈現出臨界或近于臨界的均化狀態(tài)。鹽度估計等量于濃度為84到 10.nacl溶液中鹽的含量。富礦流體(蒸汽含量占總體積的10-40)從共同成礦到成礦之后的總體，包括首次到二次夾雜在共同成礦的螢石，均化溫度的石英和鹽度 (104-33c)估計等量于濃度為32到62nacl溶液中鹽的含

8、量。事實上，這些夾雜物局部在140巴的壓力沸騰的情況下與富礦蒸汽夾雜物共存。bakel、和lang (2003)提出了巖漿熱液矽卡巖系統(tǒng)的初始條件較高的溫度 (約50o。c)，從而導致了成礦之前的巖漿流體在兩相場(不相溶的鹽水和蒸汽夾雜物)情況下的俘獲。由于傅斯麥斷層的向前運動大大改變了溫度壓力條件，這也導致了主要壓力從靜巖壓力下降到流體靜壓力(約140巴)，溫度從500。c下降到小于350。c。在低鹽度、一相場的巖漿流體 (臨界包體)情況下捕獲了流體包裹體。流體進一步發(fā)展產生了同步形成礦石，成礦后的礦石和富礦液體包體。鹵水、蒸氣、低報h蔓流體包裹體的質子激發(fā)x熒光分析在澳大利亞北賴德英聯邦科

9、學和工業(yè)研究組織(cslr)用核微探針進行了質子激發(fā)x熒光分析。ryan等人(2001)對技術的細節(jié)做了報告。表1總結了鹽水，蒸汽，臨界點和富礦液體石英包裹體的變化范圍(最大值和最小值 )和平均組成。質子激發(fā)x熒光方法的成像能力提供7在流體包裹體內元素分布的詳細計算(圖2)。正如預料的那樣，氯元素的濃度在鹵水包裹體中最高，并包含在固相之間有著明顯的優(yōu)勢;高頻分量與鉀鹽(kcl)和石鹽(由于na原子量太輕而不能做質子激發(fā) x熒光分析)相關聯。鈣、錳、鐵在液相和日前尚未確認的固相內部有出現。圍繞若汽泡的液相含有大量富礦蒸氣和臨界包體的溶質。在離析的時候，局部的富礦蒸氣包裹體和固相會被重要的液體配合

10、劑所捕獲(如混合的蒸氣鹵水包裹體)。鉛鋅的最高濃度出現在早期鹵水和蒸汽包裹體內0)3000 pm) ;后來金屬濃度會出現明顯的下降f成低鹽度的包裹休?？偟膩碚f和鉗鋅相比銅濃度在所有包體類型中是比較低的(700pm)。和鉛鋅不同，銅在鹵水包體中有最低的濃度，而在蒸氣包體中有著最高的濃度。臨界包體往往記錄著比鹵水包體更高的銅濃度；較少部分的銅產生在晚期的富礦流體包裹體內。圖2 質子激發(fā)x熒光分析圖a- 鹵水；b-蒸汽；c-臨界包體結 論對仲斯麥矽卡巖礦床中的鹵水，蒸氣，低鹽度流體包裹體的質子激發(fā)x熒光分析，認為三種流體類型都為巖漿成因。在早期的鹵水和蒸氣包體中鉛鋅的濃度最高，除此以外，礦石建造很可

11、能是低鹽度巖漿流動產生的。銅元素濃度明顯低于鉛鋅濃度，但在早期的蒸氣包體中含量最高，其中包體中硫元素復合物有可能非常重要。然而，氯化物是后期低鹽度巖漿流體的情況下形成銅元素運移的原因。數據表明，矽卡巖礦床的流體演化和一些斑巖系統(tǒng)的流體演化過程相似，兩種礦床類型中巖漿熱液流體控制著大量金屬元素的富集。表1 卑斯麥礦床鹵水、蒸汽、臨界和富礦流體包裹體pixe分析鹵水（n=9）蒸汽（n=15）臨界(n=10)富礦流體(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%)28.9345.806.181.622.840.443.119.470.484.901

12、3.891.38k (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)313472144387992155216

13、45416054615533832pb (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.

14、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- hydrotherm

15、al 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)

16、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

17、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 concen

18、tra- 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 mexi

19、co, 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. depo

20、sit 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 inc

21、lusions 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;

22、 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

23、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 (l

24、a-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

25、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

26、 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

27、 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 highl

28、ight 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 bismar

29、k 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 tempo

30、rally 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-

31、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 ha

32、ve 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

33、 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 p

34、ost-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 vap

35、or-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 inclu

36、sions.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 inclusio

37、ns). 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

38、-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 carri

39、ed 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 b

40、rine, 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) cri

41、tical 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.co

42、nclusionspixe 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-salin

43、ity 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

44、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.mean