矽卡岩和矽卡岩矿床

矽卡岩和矽卡岩矿床

Skarn and skarn deposits

常兆山

Zhaoshan Chang

Thanks to Larry Meinert

12 Nov. 2015, Xi’an, China

提纲Outline

1) Definition，mineralogy and classification

定义、矿物学和分类

2) Skarn-forming processes and evolution

矽卡岩的形成作用和演化

3)Zonation in skarn system

矽卡岩的分带

矽卡岩的勘探（小测验）

矽卡岩的定义What is a skarn? Defined by mineralogy: Ca-rich garnet and/or pyroxene

定义根据矿物组合：富钙的石榴石和/或辉石

Intrusion and

carbonate

favorable but not

necessary; not

present at type

locality

Courtesy of Larry Meinert

矽卡岩矿物Skarn mineralogy

•Garnet A32+B23+C34+O12石榴石•Pyroxene A12+B12+C24+O6辉石•Olivine A12+B14+O4橄榄石•Pyroxenoid A12+B14+O3类辉石•Epidote A22+B33+C34+O12(OH)2绿帘石•Amphibole A1+B2+C2+D4+O(OH)角闪石

May contain >20% Fe可含>20％Fe

矽卡岩矿物Skarn mineralogy Garnet石榴石A32+B23+C34+O12

Grossular钙铝榴石Ca3Al2(SiO4)3

Andradite钙铁榴石Ca3Fe2(SiO4)3

Grandite

Spessartine锰铝榴石Mn3Al2(SiO4)3 Almandine铁铝榴石Fe3Al2(SiO4)3 Pyrope 镁铝榴石Mg3Al2(SiO4)3Subcalcic garnet

CaMgSi

CaFe Si

CaMnSi

Courtesy of Larry Meinert 石榴石和辉石成分的图示

Garnet and pyroxene composition diagrams 不适用的辉石成分图

Inappropriate pyroxene composition diagram矽卡岩分类Classification of skarns

Major economic metal:主要成矿元素

-Fe, Cu, Pb-Zn, Au, W, Sn, Mo

Magnetite is abundant in many types:

大量磁铁矿存在于多种矽卡岩中

矽卡岩分类Classification of skarns Ca-skarn:钙矽卡岩

-Garnet, pyroxene, vesuvianite, epidote, chlorite …

-石榴石，辉石，符山石，绿帘石，绿泥石…

Mg-skarn:镁矽卡岩

-Olivine, humite, phlogopite, chlorite, serpentine, talc

-橄榄石，硅镁石，金云母，绿泥石，蛇纹石，滑石等

矽卡岩分类Classification of skarns Endoskarn vs. exoskarn:内矽卡岩–外矽卡岩

Exoskarn is typically much more abundant than endoskarn: 外矽卡岩通常比内矽卡岩广泛得多

矽卡岩的形成作用Skarn-forming processes

Magmas

contain

volatiles (H2O,

CO2, HCl …)

岩浆中总含有挥

发份（H

2O,

CO2, HCl ...,)矽卡岩的形成作用

Skarn-forming

processes

The volatile will separate out upon

depressurization and/or

crystallization挥发份会通过岩浆

减压和/或重结晶分离出来

Water in melt

水溶于岩浆

Magmatic

Hydrothermal

fluid 岩浆热液

Second boiling

第二类沸腾

First boiling

第一类沸腾

水在岩浆中的溶解度和分离Water solubility and

exsolution

Burnham (1979, 1981, 1997)Water dissolved in

melt

Water in aqueous phase -Magmatic

Hydrothermal fluid

Carbonate-rich area: magma assimilates carbonate →CO 2increases →H 2O

solubility decreases →exsolution occurs earlier (Meinert, 1995)碳酸盐岩地区：岩浆吸收碳酸盐→CO 2增加→H 2O 溶解度降低→水在岩浆结晶早期就开始分离出来(Meinert, 1995)

Fumarole, >850 C vapors

火山喷气孔，气体温度>850°C

White Island, New Zealand; Courtesy of Jeff Hedenquist

High temperature degassing not uncommon

现代火山附近高温水汽并不少见

矽卡岩的形成作用Skarn-forming processes

Such magmatic hydrothermal fluids are rich in Si and Fe. Al is normally low except where there is high F

这样的岩浆热液含大量硅和铁。铝一般较低，除非热液富氟。

Sn-associated Mole granite; Audetat et al., 2000

Fe up to 21.6 wt%

Empire Cu-Zn skarn; Chang and Meinert, 2004

Evolution of skarns –1a 矽卡岩的演化–1a

Thermal metamorphism -isochemical:热变质; 等化学；无物质带入带出

-Marble, hornfels

大理岩，角岩

Meinert, 1992

Before magmatic water is released from magma

chamber; no fluid flow 此时岩浆水还没有从岩浆房中释放出来，没有流体流动