Date of Award

1980

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Geology

Abstract

The Tinton area breccia crops out in two areas in the northern Black Hills just northwest of Tinton, South Dakota, in an area of Precambrian metamorphic rocks, pegmatites, and Tertiary intrusives. The outcrops are fairly circular, the smaller measuring 150 meters and the larger measuring 400 meters. Located nearby is the Mineral Hill alkalic ring dike complex, with which this breccia is thought to be associated.

The breccia contains clasts of diverse rock types set in a fine-grained igneous matrix with a chemistry in the quartz latite to rhyodacite range. The rock types present within the clasts are, in order of decreasing abundance: pegmatite, amphibolite, monzonite porphyry, metamorphosed anorthosite, quartz latite, muscovite-biotite? schist?, graphite schist, and a separate category of highly altered clasts. The clasts are 0.1 to 10 cm in diameter; they are well mixed and many are rounded. Both clasts and matrix are hydrothermally altered and fractured, and small-scale faulting is common with deposition of sulfides in many fractures.

Four possibilities for an origin of this breccia are: igneous intrusion breccia, pyroclastic volcanic breccia, meteorite impact breccia, and. breccia pipe. The presence of well mixed, rounded clasts of diverse lithology and size that are highly altered and fractured point to a probable breccia pipe origin. As an inferred stock of magma at depth cooled, it probably evolved gases which initiated a breccia pipe sequence to the surface.

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