Mineral Resources Potential - Geothermal Resources

Metallic Mincrals 43
quartz schists, carbonaceous mica-schists, amphibolites and basic
to ultrabasic rocks. This unit is separated from footwall biotite
gneiss by a major shear zone. The ore bodies are hosted in the
volcano-sedimentary sequence and colisist of swarms of quartz
veins, lenses, and stockworks that propagated along mesoscale
dude to brittle-ductile shear;zones. The lithology of the facies
occurring in the Legadembi deposit and surrounding area is briefly
described below (Fig. 5).
(i) Quartz-feldspar-mica-schist; gold mineralization at: the
Legadembi mine occurs in quartz0 feldspathic mica-schist, and to
some extent in actinolite-treinolite-hornblende schist. The schists
are bounded to the east by non-mineralized biotite-quartzo-
feldspathic gneiss and to the west by meta-gabbro. All these units
dip at approximately 70" to the best and strike N-S direction. The
quartzo-feldspathic mica-schist is about 1 00 rn thick. pinching out
to the south. In the mine area, it occurs as discontinuous thrust-
nappes units. It is composed of quartz, sericite, graphite, biotite,
and plagioclase with disseminated sulphides. Biotite schist is
dominant, but not the only host for gold mineralization;
(ii) Biotite gneiss; this unit occurs to the east and adjacent to the
eastern side of the Legadelnbi deposit, forming the footwall of the
Legadembi-Sakaro thrust sequence. It is strongly foliated and
contains porphyrodasts of quartz and feldspar. The only alteration
seen in this biotite gneiss unit consists of minor quartz-sericite
along the contact with the ultramafic rocks to the west;
(iii) Ultramafic rocks; these rocks are strongly altered to chlorite-
talc and tremolite-actinolite-talc rocks, with lesser chlorite schist,
tremolite-actindite schist and graphitic quartz-mica-actinolite
schist. They define the major shear zone that separates the upper
greenschist facies meta-volcano-sedimentary sequence of the
Megado Terrain from the upper arnphibolite facies gneisses. The
altered meta-ultramafic rocks locally contain quartz veins that host
gold mineraIization;