『Abstract
Germanium (Ge) is a scarce, but not an extremely rare element
in the Earth's crust (about 1.6 ppm Ge crustal average). Principal
geochemical substitutions and mineral associations of Ge include
Si, C, Zn, cu, Fe, Sn, and Ag. Most Ge is dispersed through silicate
minerals due to the substitution of Ge4+ for the geochemically
similar Si4+. Ge is unusual in that it exhibits siderophile,
lithophile, chalcophile and organophile behaviour in different
geologic environments. Only minor variations in Ge concentrations
are known from different igneous rocks, siliceous sedimentary
rocks, and their metamorphic equivalents. Carbonates and evaporites
show a depletion to the crustal average of Ge. There is a tendency
for Ge to be slightly enriched in silicate minerals of late magmatic
differentiates (e.g., muscovite granites), rocks that crystallize
in the presence of a high volatile concentration (e.g., pegmatites,
greisens) and late hydrothermal fluids, accounting for ore deposits.
Ge does not form specific ore deposits; rather it occurs in trace
and minor amounts in various ore deposit types. Grades of a few
tens to several hundred ppm Ge are known in sulphide deposits:
volcanic-hosted, massive sulphide Cu-Zn (-Pb) (-Ba) deposits;
porphyry and vein-stockwork Cu-Mo-Au deposits; porphyry and vein-stockwork
Sn-Ag deposits; vein-type Ag-Pb-Zn deposits; sediment-hosted,
massive sulphide Zn-Pb-Cu (-Ba) deposits; carbonate-hosted Zn-Pb
deposits, and polymetallic,Kipushi-type Cu-Pb-Zn-Ge deposits.
Low-iron sphalerite is the most important of all minerals containing
Ge. Other sulphur minerals, e.g., enargite, bornite, tennantite-tetrahedrite,
luzonite, sulvanite, and colusite, are significant Ge sources
in some deposits. At high S activities, the thiocomplex [GeS4]4- can give rise to the formation
of thiogermanate minerals, e.g., argyrodite, briartite, renierite,
and germanite, which can form elevated Ge concentrations, above
all in Kipushi-type deposits. Ge concentrations due to sorption
processes in iron hydroxides and oxides refer to those in oxidation
zones of sulphide ore deposits, especially at the Apex Mine, USA,
and Tsumeb, Namibia, as well as to iron oxide ores, particularly
in banded iron formation (BIF). Lignite and coal deposits show
germanium grades that vary several orders of magnitude, both regionally
and within particular deposits, from levels less than the Ge abundance
in the Earth's crust up to a few thousands ppm Ge. This Ge enrichment
is effected by chemisorptive processes on relatively stable organo-complexes,
e.g., lignin and humic acids.
Currently, Ge is recovered as a by-product from sphalerite ores,
especially from sediment-hosted, massive Zn-Pb-Cu (-Ba) deposits
and carbonate-hosted Zn-Pb deposits, from polymetallic Kipushi-type
deposits, and lignite and coal deposits in China and Russia. Figures
for worldwide Ge reserves are not available.
Keywords: Germanium; Metallogenesis; Mineralogy; Geochemistry;
Ore deposits』
Contents
1. Introduction
2. Distribution
2.1. Germanium hydrogeochemistry
2.2. Mineralogy and crystal chemistry
3. Geochemistry
4. Geological setting of Ge-bearing deposits
4.1. Volcanic-hosted massive sulphide (VHMS) Cu-Zn (-Pb)
(-Ba) deposits
4.2. Porphyry and vein-stockwork Cu-Mo-Au deposits
4.3. Porphyry and vein-stockwork Sn-Ag deposits
4.4. Vein-type Ag-Pb-Zn (-Cu) deposits
4.5. Sediment-hosted massive sulphide (SHMS) Zn-Pb-Cu (-Ba) deposits
4.6. Carbonate-hosted base metal deposits
4.6.1. Mississippi Valley-type (MVT) Zn-Pb-Fe (-Cu) (-Ba) (-F)
deposits
4.6.2. Irish-type (IRT) Zn-Pb (-Ag) (-Ba) deposits
4.6.3. Alpine-type (APT) Zn-Pb deposits
4.6.4. Kipushi-type (KPT) polymetallic deposits
4.6.5. Germanium in oxidation zones of Kipushi-type deposits
4.6.6. Sediment-hosted stratiform Copper (SSC) deposits
4.7. Germanium in non-sulphide Zn-Pb deposits
4.8. Germanium in Fe-oxide ores
4.9. Germanium in coal and lignite deposits
5. Summary and conclusions
Acknowledgements
References