Mineralization occurs either as structurally controlled veins and breccias discordant to the stratigraphy and less commonly as stratabound mineralization either in extrusive rocks or permeable sedimentary facies.
12.
The primary igneous rock on the Wrekin is rhyolite; this has a pinkish colour and is usually banded as it is a slow cooling viscous extrusive rock.
13.
To the south near Lake Superior, rock strata of the Duluth and Beaver Bay complexes are interspersed with and underlie the extrusive rock of the North Shore Volcanic Group.
14.
The term quartz keratophyre has traditionally been used in the Nordic countries to describe a metamorphosed, felsic extrusive rock, corresponding to rhyolite, dacite, or rhyodacite according to IUGS terminology.
15.
Igneous rocks are divided into two main categories : extrusive rocks result from magma reaching the surface either as lava or " fragmental ejecta ", forming minerals such as pumice or basalt.
16.
Differential weathering of a series of igneous intrusions has yielded a number of prominent hills in the landscape, most notably the Craigie and Broughty Ferry, the bedrock geology is of extrusive rocks, including mafic lava and tuff.
17.
The volcano is part of the so-called " Tin belt ", a territory in the Andes where large tin mineral deposits are found in granitic and extrusive rocks, formed from sulfidation reactions involving the numerous volcanoes in the area.
18.
Extrusive rocks ( such as basalt, rhyolite, andesite and obsidian ) and intrusive rocks ( such as granite, granodiorite, gabbro and peridotite ) contain primary minerals including quartz, feldspar, plagioclase, muscovite, biotite, amphibole, pyroxene and olivine in varying concentrations.
19.
The complete sedimentary sequence is separated in Lupata region, about 10 km southeast of Monte Muambe, in Chincongolo area, near to Lupata Gorge, and consists of Upper Lupata Sandstones formation, intrusive rocks ( syenite ), carbonatites ( intrusive and effusive products ) and alkaline extrusive rocks.
