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發(fā)表于 2010-6-17 16:25
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本帖最后由 一臉褶子 于 2011-1-18 08:59 編輯
2010年南京大學(xué)礦床學(xué)復(fù)試筆試部分——地院面包提供
專業(yè)綜合測試（任選三題）
1、? ?? ???簡述矽卡巖礦床的形成過程
2、? ?? ???論述岡底斯帶斑巖型銅礦與環(huán)太平洋帶斑巖型銅礦的異同之處？
3、? ?? ???你是如何理解“中國東部中生代成礦大爆發(fā)”的？舉例說明
4、? ?? ???海底噴流熱液硫化物礦床的基本地質(zhì)特征和分類？
專業(yè)英語：
翻譯“fluid and source magma evolution of the Questa porphyry Mo deposit, New Mexico, USA”的Abstract 和Introduction部分。
Fluid and source magma evolution of the Questa porphyry Mo deposit, New Mexico, USA
Abstract
Combined fluid inclusion microthemometry and microanalysisi by laser ablation inductively coupled plasma mass spectrometry are used to constrain the hydrothermal processes forming a typical climax type porphyry Mo deposit.
Molybdenum mineralization at Questa occurred in two superimposed hydrothermal stages, a magmatic-hydrothermal breccia and later stockwork veining.in both stages, texturally earliest fluids were single-phase, of low salinity(~7wt% Nacl) and intermediate-density.Upon decompression to ~300bar, they boiled off a vapour phase ,leaving behind a residual brine (uo to 45 wt% Nacl)at temperature of~420℃。The highest average Mo concentrations in this hot brine were ~500μg/g,exceeding the Mo content of the intermediate-density input fluid by about an orden of magnitude and reflecting pre-concentraition of Mo by fluid phase separation prior to MoS2 deposition from the brine. Molybdenum concentration in brine inclusions ,then, decrease down to 5μg/g,recording Mo precipitation in response to cooling of the saline liquid to ~360℃.Molybdemite precipitation from a dense,residual and probably sulphide-depleted brine is proposed to explain the tabular shape of the ore body ande the absence of Cu-Fe sulphides in contrast to the more common Cu-Mo deposits related to porphyry stocks. Cesium and Rb concentrations in the single-phase fluids of the breccia range from 2 to 8 and from 40 to 65μg/g,repectively. In the stockwork veins,Cs and Rb are incompatible and hydrothermally non-reactive elements,the systematic increase in their concentration requires two distincr pules of fluid exsolution from a progressively more fractionated magma.
By contrast,major element and ore metal concentrations of these two fluid pulses remain essentially constant.Mass ICPMS suggest that at least 25 KM3 of melt and 7 Gt of deep input fluid were necessary to provide the amout of Mo contained in the stockwork vein stage alone.While the absolute amounts of fluid and melt are uncertain,the well-constrained element ratios in the fluids to gether with empitical fluid/melt pattition coefficients derived from
the inclution analyses suggest a high water content of the evidence,these results suggest that initial fluid exsolution may have occurred at a confining pressure exceeding 5kbar.
The source of the molybdenum-mineralising fluids probably was a particularly large magma chamber that crystallized and fractionsted in the lower crust or at mid-crustal level,well below the shallow intrusions immediately underlying Qusta and other porphyry molybdenum deposits.
Keywords porphyry molybdenum fluid inclusion Questa
Introduction
The global molybdenum supply is almost completely mined from porphyry-type ore deposit.climax-tpe porphyry Mo deposits are the most important sources and reserves,after Mo obtained as a valuable by-product of porphyry-Cu-Mo deposits such as Chuquicamata,El Teniente and Bingham but at much higher grades.they represent an end member of dances of Mo and F,but virtually no Cu and Au.the deposits are associated with shallow intrusions of high-mainly along the North American Cordillera.Major deposits of this type are Climax,Colorado,Urad-Henderson,Colorado andQuesta,New Mexico,all three being located in a single major province in the southwestern USA.Lead isotopes revealed a lower-crustal origin(partial melting of biotite-beating felsic granulite)of the magmas from which the Climax-type deposits in the southwestern USA formed.
The chemical composition and the evolution of the magmatic-hydrothermal fluids are key to understanding the origin of metals and precipitation mechanisms in this type of deposit and slso in Mo-depositing stages of ordinary Cu-Mo porphyries.The aim of this study is to investigate the compositional evolution of the ore-forming composition of the magmatic source versus the influence metal budget of the deposit.the Questa deposit,presently mined by Molycorp Inc.,provides an excellent and mineralogy are comparatively simple,and much of the sample material contains free-grown quartz crystals ideal for fluid inclusion studies.Standard microscopic and microthermometric procedures combined with laser ablation inductively coupled plasma mass spectrometry(LA-ICPMS)were used to determine the physico-chemical properties of the ore-forming fluids and to investigate ore-forming process.
The geology and petrography of the Questa Mo deposit and its surroundings has been studied e.g. by Ishihara(1967),Langhlin et al.(1969),Lipman eti al.(1986),Johnson and Lipman(1988),Johnson et al.(1990)and Czamanske et al.(1990).Most recently,Ross et al.(2002)described the textural,petrographic and mineralogical zonation of the magmatic-hyduotherman breccia(MHBX),which hosts the main ore bodies.Earlier fluid inclusion studies led to the recognition of essentislly liquid-rich, low-salinity inclusionsand liquid-rich,low-to-moderate-salinity inclusions.the brine was interpreted as having exsolved directly from the magma,based on an apparent lack of coeval vapour.A recent fluid inclusion study by ROWE(2005)identified fluid phase separation in the system and interpreted brine inclusions homogenizing by halite dissolution to be an effect of accidental entrapment of halite.magma mixing generation of metal-rich fluids at Questa(Jones 2002),but it remains unclear whether a selectively Mo-enriched precursor magma is ultimately required for Mo ore formation.Oxygen and hydrogen isotopes and gas analyses(Ar-He-N2)demonstrate that the ore-froming fluid at Questa are of magmatic origin with negligible meteoric component and that all facies of the breccia ahd the stockwork veins are chemically and isotopically identical.Analysis of co-existing fluid and melt inclusions from miarolitic cavities of two barren intrusions within the Questa caldera has provided fluid-melt partition coefficiengs for a number of elements,linked to the degree of crystallization of the magma at the time of local fluid exsolution(Audetat snd Pettke 2003)
南京大學(xué)礦床學(xué)2011回憶版
1.試述矽卡巖礦床的成礦過程（35）
2.簡述Cu-Ni硫化物礦床的成礦特征，成礦作用（35）
3.闡述淺成低溫?zé)嵋篈u-Ag-Cu礦床的分類類型及主要地質(zhì)特征（35）
4.分析斑巖型銅礦床的成礦特征，成礦巖體特征及全球成礦規(guī)律（45）
注：個別詞匯可能有出路，大體內(nèi)容就是這些
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發(fā)表于 2010-1-28 13:43
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