Tachov
The Lučina dam
The area west of Tachov is built by rocks of the Varied group of the Český les Moldanubicum, which are metamorphosed deposits of a Proterozoic sea. From the original fine-grained and calcareous sediments, penetrated by effusions of basic lavas, formed biotite- and graphite paragneisses, crystalline limestones, erlans and amphibolites.
Cliff near dam
Very widespread amphibolites make several tens to hundreds meter thick layers in paragneisses. They have most frequently a markedly banded texture, caused by rhythmical alternation of several millimeters- to centimeter thick dark strips with prevailing amphibole and strips of greenish grey erlans. Amphibolites formed during regional metamorphism of magmatic rocks, mainly basalts, at temperatures 500 – 700°C, i.e. conditions, which govern in depths 10 – 30 km bellow the Earth surface. Also biotite rich gneiss bands and solitary strips of light green compact epidotite can be observed.
Veins in the rock
The diversity of amphibolite bodies is enhanced by abundant dikes and sills of leucocratic and aplitic granites, quartz lenses and pegmatite bodies. To the amphibolites are spatially bound limestone bodies, which were extracted in the past as a raw material for local limekilns. Crystalline limestones are whitish gray, foliated, fine-grained and they contain abundant erlan partings. Also mineral composition of these metamorphosed limestones is interesting. Their main mineral is calcite, but significant are also diopside, wollastonite, plagioclase feldspars (oligoclase, andesine and labradorite), potassium feldspars like orthoclase and microcline, and also garnet. We find rarely more minerals in the marbles: titanite, apatite and pyrrhotite. Two hollows after limestone extraction are also in the territory of the ceased village Lučina between Milíře and Mýto. They are known as Račí rybníky (“crawfish ponds”). Amphibolites are suitable for production of crushed rock and they were mined in the past in a quarry on the foothill of Mýtský kopec at the influx of the Lužní potok brook into the Lučina river dam. Now they form a portion of the earthen dam of the barrage, which serves as a drinking water reservoir for the Tachov area.
Low water level
