Old Lead Belt, Fredericktown - Bonne Terre, Doe Run, Park Hills, Desloge, Leadwood, La Motte

Missouri, USA

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The Old Lead Belt of south-eastern Missouri, USA, is located on the north-eastern flanks of the Precambrian basement high of the St. Francois Mountains.   It includes the Fredericktown, Bonne Terre, Doe Run, Park Hills, Flat River, Desloge, Leadwood and other mines. These mines are distributed over two blocks of continuous to semi-continuous mineralisation. The Bonne Terre block to the NE trends NE-SW over a length of ~6 km and width of ~1.5 km. The second, larger block to the SW, which is centred on the Flat River, Deslodge and Leadwood mines is nearly 20 km long, and 1 to 6 km wide, wrapped around the St. Francois Mountains basement block, trending from north-south in the SE to WNW-ESE in the NW.

Underground mining took place at Bonne Terre from 1864 to 1961, at Doe Run from 1887 to 1914, in Desloge from 1929 to 1958 and at Leadwood from 1915 to 1962. The final operation, at Park Hills, closed in 1972. Galena was the principal ore mineral. Ore occurred throughout the 120 m thick Bonneterre dolomites, and extended for as much as 30 m into the underlying Lamotte sandstones.

The smaller Fredericktown cluster of mines, including the La Motte mine, is some ~30 km to the SE, on the eastern margin of the St. Francois Mountains basement block, surrounded by a swarm of basement knobs protruding through the Cambrian host sequence.

In the Fredericktown district, ore was generally shallow - usually 75 to 120 m from the surface. Deposits were relatively flat-lying, sinuous lenses up to 12 m thick, 15 to 75 m wide and several hundred metres long. Ore was restricted to the lower 15 m of the Bonneterre Formation and the upper 5 m of the Lamotte Sandstone (Snyder and Gerdemann, 1968).

These deposits are some 40 km NE of the centre of the Viburnum Trend and occur in a very similar stratigraphic position and lithologic setting, with comparable ore styles to the deposits of that trend.

See the separate Southeast Missouri Iron District record for regional setting, and the Viburnum Trend record for the district stratigraphy and occurrence of mineralisation.

While in most respects, the mineralisation at the Viburnum Trend and Old Lead Belt is very similar, there are differences (Ohle, 1990). In the Old Lead Belt, mineralisation is predominantly within the transition from the mid to upper Cambrian Lamotte Sandstone (which unconformably overlies the Mesoproterozoic granite-volcanic basement) and the lower 20 m of the overlying Upper Cambrian Bonneterre Formation carbonates. Mineralisation was prevented from forming in stratigraphically higher units by impervious layers in the upper Bonneterre and the immediately overlying Davis Formation, an aquitard whose low-permeability shales and carbonates impeded the ascent of mineralising fluids (Appold et al., 2004). In contrast, on the Viburnum Trend, although mineralisation occurs throughout the Bonneterre Formation, most is in the upper 25 m below the base of the Davis Formation.

Galena in the Old Lead Belt (except at Bonne Terre) occurred as disseminated, relatively small grains scattered through the lower half of the Bonneterre Formation, with galena replacing dolomite, ad occurring along bedding-plane contacts, in fracture zones and less frequently as breccia cement. Individual ore bodies spread laterally for hundreds of metres and vertically up to 60 m. Solution collapse breccias and open-space filling was virtually absent, although similar structures are evident at both districts. In contrast, on the Viburnum Trend, much of the ore occurs as large crystals that occupy vugs of various sizes and in solution collapse breccias.

The important ore controls in the Old Lead Belt are predominantly sedimentary, where depositional characteristics, particularly permeability, influenced ore distribution which spread over wide areas laterally in "favourable beds". These include NE-trending quartz-sand and calcarenite bars or ridges, and superposed algal reef structures (Hagni, 1989). On the Viburnum Trend, the processes were more intense, allowing mineralisation to cross-cut stratigraphy via structural ground preparation.

The mineral assemblages in both areas are virtually the same, although zinc and copper occur in much more significant concentrations in parts of the Viburnum Trend. Copper sulphides, other than chalcopyrite, were not recorded in the Old Lead Belt, but are abundant on the Viburnum Trend. Similarly, drusy quartz is common on the Viburnum Trend, but absent in the Old Lead Belt.

The largely stratabound, but epigenetic deposits of the Old Lead Belt and the Viburnum Trend are noted for the predominance of lead and the elevated levels of copper, cobalt and nickel compared to other carbonate hosted base metal deposits. Ore deposition commenced with the Cu and Co rich mineralisation (chalcopyrite and bornite), followed by the main stage fine galena and minor sphalerite, and the minor vug filling late stage coarsely crystalline galena.

Total historic production from the exhausted districts, mined out between 1720 until 1972, (Doe Run presentation, 2012) were:
      Old Lead Belt (main zone to the north) - 240 Mt @ 2.9% Pb, 0.3% Zn (Historic Production 1864 to 1972)
      Fredericktown (~30 km SE of the Old Lead Belt) - 15 Mt @ 3.9% Pb (Historic Production 1720 to 1961).

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1989.     Record last updated: 25/8/2013
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Goldhaber M B, Church S E, Doe B R, Aleinifoff J N, Brannon J C, Podosek F A, Mosier E L, Taylor C D, Gent C A  1995 - Lead and Sulfur isotope investigation of Paleozoic sedimentary rocks from the southern midcontinent of the United States: implications for paleohydrology and ore genesis of the southeast Missouri Lead belts: in    Econ. Geol.   v 90 pp 1875-1910

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