Hydrothermal Deposits - Metals and Society: An Introduction to Economic Geology - page 100

many hundreds of square kilometers and contain numerous small to large deposits.
The limits of an ore district are defined by geologic features, most notably the
presence of breccias, facies changes from shale to carbonate at basin margins, large
faults and basement highs.
The deposits are mineralogically simple; dominant minerals are sphalerite,
galena, pyrite, marcasite, dolomite, calcite, and quartz. Sulfide mineral textures
are extremely varied, ranging from coarse and crystalline to fine-grained, massive
to disseminated. Banded and colloform structures typical of deposition in open
spaces from fluids are found in some deposits (Box 4.5). Alteration associated with
ore bodies consists mainly of dolomitization, brecciation, host-rock dissolution,
and the dissolution or recrystallization of feldspar and clay. Evidence of dissolution
of carbonate host rocks, expressed as slumping, collapse or brecciation, is common.
Box 4.5 The Missouri-Mississippi Valley Mining District
(a) Brecciated ore from the Robb Lake MVT deposit in Canada. A matrix of sphalerite and
galena encloses fragments of dolomite. (b) Colliform ore from the Cadjibut mine in
Australia (Photo - Chris Arndt) .
During the last centuries, the mining industry has been important for the
economic and social fabric of several states of central USA and especially for
Missouri. Pierre Charles LeSeur, a Frenchman, first prospected in the