Petrology and mineralogy of certain portions of the Fredericktown deposits
type: CreativeWork
description: "The Fredericktown area is part of the 'Lead Belt' district of southeastern Missouri, the major lead-producing region in the world for fifty years. The district is a typical example of the Mississippi Valley Type deposits. The ores occur in Upper Cambrian sediments overlying Precambrian rocks. The Fe-Cu-Pb-Zn (-Co-Ni) - sulphide deposits of Fredericktown occur over a few square kilometers in sediments overlying two 'granite knobs'. The sedimentary units lap upon and pinch-out against these buried basement hills. The basal sedimentary unit, the Lamotte Formation, is a time-transgressive, marine, submature orthoquartzite. It contains a Boulder Bed at the base or at intermediate levels. Occasional shale and arkosic sandstone bands are interlayered with the sandstone. A Transition Zone separates the Lamotte from the Overlying Bonneterre lithofacies and shows a slight unconformity. This zone is essentially a polymict greywacke sandstone with some lamination of glauconitic shale and dolomitic limestone. It contains most of the sulphide ore body. The sulphides occur in solid layered patterns, as disseminated agglomerations, concretions, individual grains, and as fragments of grains. They display distinct polar features that serve as top-bottom indicators, connoting depositional and/or diagenetic accumulation. In the Bonneterre dolomitic limestone, massive sulphide layers predominate. However, some sulphides, especially galena, occur in form of veinlets and other cross-cutting structures. Disruption features often contain galena, and transitions from these to complete brecciation of the monogenic type exist. Galena also exhibits diagenetic recrystallization as well as corrosion features. The geometric relations between the sulphides are used for: l) The classification of 4575 bravoite-pyrite grains into eight types. Abrupt or nongradational zoning and unindirectional-gradational or solid solution zoning are present. Both can form under the same conditions; 2) The statistica…
abstract: "The Fredericktown area is part of the 'Lead Belt' district of southeastern Missouri, the major lead-producing region in the world for fifty years. The district is a typical example of the Mississippi Valley Type deposits. The ores occur in Upper Cambrian sediments overlying Precambrian rocks. The Fe-Cu-Pb-Zn (-Co-Ni) - sulphide deposits of Fredericktown occur over a few square kilometers in sediments overlying two 'granite knobs'. The sedimentary units lap upon and pinch-out against these buried basement hills. The basal sedimentary unit, the Lamotte Formation, is a time-transgressive, marine, submature orthoquartzite. It contains a Boulder Bed at the base or at intermediate levels. Occasional shale and arkosic sandstone bands are interlayered with the sandstone. A Transition Zone separates the Lamotte from the Overlying Bonneterre lithofacies and shows a slight unconformity. This zone is essentially a polymict greywacke sandstone with some lamination of glauconitic shale and dolomitic limestone. It contains most of the sulphide ore body. The sulphides occur in solid layered patterns, as disseminated agglomerations, concretions, individual grains, and as fragments of grains. They display distinct polar features that serve as top-bottom indicators, connoting depositional and/or diagenetic accumulation. In the Bonneterre dolomitic limestone, massive sulphide layers predominate. However, some sulphides, especially galena, occur in form of veinlets and other cross-cutting structures. Disruption features often contain galena, and transitions from these to complete brecciation of the monogenic type exist. Galena also exhibits diagenetic recrystallization as well as corrosion features. The geometric relations between the sulphides are used for: l) The classification of 4575 bravoite-pyrite grains into eight types. Abrupt or nongradational zoning and unindirectional-gradational or solid solution zoning are present. Both can form under the same conditions; 2) The statistica…
author: El Baz, Farouk
keywords: Geology
date published: 2016-02-10T08:00:00Z
date modified: 2026-07-24T03:18:09Z
provider: Missouri University of Science and Technology
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Missouri at Rolla