Geology of the RC Westfork Cemetery Ridge Solution Collapse Breccia, Viburnum Trend, Southeast Missouri. By Thomas Schott

Transcription

1 Geology of the RC Westfork Cemetery Ridge Solution Collapse Breccia, Viburnum Trend, Southeast Missouri By Thomas Schott

2 Introduction Viburnum Trend Pb-Zn mineralization is blind Historically poor results of Geophysical/Geochemical methods Poor or incomplete logging and retention of drill core Change in logging process identified existence of solution collapse breccias above Bonneterre Formation Davis, Derby-DoeRun, and locally Potosi Formations maybe altered and brecciated Result: Recognition of a structural and alteration halo above ore-bearing breccia trends in the Bonneterre has aided exploration

3 Southeast Missouri MVT Subdistricts Historic Production 1720-Present: ~611M Tons and Counting Indian Creek M Tons at 3.6% Pb 0.4 % Zn 0.1% Cu Old Lead Belt ` 263 M Tons at 2.9% 0.3% Zn Viburnum Trend 1960-Present 300 M Tons at 5.8% Pb 1.1% Zn 0.3% Cu Fredericktown Mine LaMotte M Tons at 3.9% Pb St. Francois Mountains Annapolis M Tons at 2.3% Pb RC-Westfork Cemetery Ridge Resource N 10 Miles MISSOURI

4 Contours of the top of the Lamotte Formation Fletcher Mine 850 ft elev. 770 ft elev. 790 ft elev. 810 ft elev. 830 ft elev. 850 ft elev. 830 ft elev. 810 ft elev. RC Westfork Cemetery Ridge Orebody Axis of the buried Precambrian Ridge 790 ft elev. Sweetwater Mine Note: Contours are relative to sea level with 1000 feet added. 790 ft elev. 810 ft elev. N 500 ft

5 Generalized Geologic Cross-section of the RC Westfork Cemetery Ridge Breccia trend W-E Cross-section looking north Residuum: 0 to +300 Thick Variably oxidized and bleached Potosi Fm; locally with heavy Calcite as fracture and breccia fill Potosi Formation: +/- 350 Thick Zone of Bleaching & Oxidization; Locally with solution collapse brecciaiton Derby-Doe Run Formation: +/- 90 Thick FeS2 mineralization (marcasite>>pyrite) NiS mineralization (predom. millerite) ZnS mineralization (cubic stage sphalerite) Davis Fm 100% Dolomitized Zone of Davis carbonates exhibiting dolomitization and dissolution; solution collapse brecciation common Davis Formation: Average thickness +/-165 Locally thinned to 120 in gut of breccia trend Mineralized Pb-Zn Halo 1GS Marker Bed Upper 5 Zone 5 PM Marker Bed Lower 5 Zone 5/7 Zone Ore; Pb : Zn = 7.6 : 1 Ore; Pb : Zn = 6.9 : 1 Ore; Pb : Zn = 3.2 : 1 Down-Dropped Davis shale Tee-Pee shaped bounding faults Bonneterre Formation: Average thickness +/- 330 Locally thinned to 280 in gut of breccia trend in upper ½ of Bonneterre 7 Zone Reef 3/4 Zone White Rock 10 Zone 12 Zone 19 Zone (Sandy dolomite transition) Lamotte Formation

6 Diamond drill hole showing galena-sphalerite mineralization with leached octahedral galena molds and 2ndary white dolomite Headline here Use this slide for plain text Zone of octahedral galena dissolution White Secondary dolomite 15.7 feet at 12.25% Pb 4.11% Zn and 0.82 opt Ag Zone of heavy sphalerite mineralization

7 Pillar in the RC Westfork Overcut Showing Solution Collapse Brecciation in the Upper 5 Zone Collapsed and rotated blocks of brown, oolitic dolomite in a matrix of late stage cubic galena

8 Diamond drill hole showing down-dropped Davis shale Formation in 1 zone Bonneterre Bonneterre 1 zone Down-dropped section of brecciated, dolomitic Davis shale Bonneterre 1 zone

9 Diamond drill hole 2000 feet east of the Cemetery Ridge Breccia Trend showing the unaltered nature of Davis Fm. Green, fissile shale w/ interbedded limey mudstone bands and mottled gray-brown, locally oolitic, xtln limestone

10 Percent (%) Dolomitization of carbonates in the Davis Formation Fletcher Mine RC Westfork Cemetery Ridge Orebody Zone of Limey Davis; Solution Collapse Brecciation restricted to Bonneterre only. >90% dolomite in Davis >75% dolomite in Davis >50% dolomite in Davis >25% dolomite in Davis Solution collapse brecciation extends up into Davis Fm and locally DDR Fm. Zone of Limey Davis; Solution Collapse Brecciation restricted to Bonneterre only. Sweetwater Mine N 500 ft

11 Diamond drill hole showing dolomitization and thinning of Carbonates with heavy FeS2 mineralization in the upper Davis Fm Carbonates in Davis Fm completely altered to dolomite followed By subsequent carbonate dissolution and collapse. 2.7 at 0.1% Pb --% Zn --% Cu 17.3% Fe 0.22 opt Ag Iron Cap consisting of marcasite >> pyrite as disseminations, fracture fill, bands, and breccia matrix fill

12 Distribution of iron sulfides in the Davis and Derby-Doe Run Formations Fletcher Mine Extent of strong iron sulfide (marcasite>>pyrite) mineralization (in yellow). FeS2 as locally heavy dissemniations, bands, fracture fill, and as breccia matrix. RC Westfork Cemetery Ridge Breccia trend (in red) Extent of trace iron sulfide (marcasite>>pyrite) mineralization (in orange). FeS2 as scattered trace Disseminations and rare fracture fill. Sweetwater Mine N 500 ft

13 Diamond drill hole showing massive solution collapse brecciation in the Davis Shale Hole 09W59 from the gut of the Cemetery Ridge breccia Showing massive solution collapse brecciation in the Davis Fm Solution collapse breccia Thinned, tilted, broken beds of gray dolomite In a green shale matrix Massive heterolithic solution collapse brecciation

14 Diamond drill hole showing tilted bedding and solution collapse brecciation in the lower Derby-DoeRun (DDR) Fm Dimly crackled brecciated dolomite Tilted bedding in DDR at 50 Degrees CA Dimly brecciated DDR Tilted bedding Dimly brecciated DDR Tilted bedding in DDR at 50 Degrees CA

15 Conclusions Historically poor results of Geophysical/Geochemical methods Poor or incomplete logging and retention of samples In 2000 change in logging process identified existence of solution collapse breccias beyond Bonnterre Davis, Derby-DoeRun, and locally Potosi Formations maybe altered and brecciated This resulted in an updated geologic model which has facilitated exploration in a mature district.

16 Conclusions Continued Key points: Mine exploration data as well as you mine ore body. Geologic models are not static; revise and update. Apply new geophysical/geochemical technologies as they become available. The sun setting on a historic mine district can be postponed by wise use of your exploration resources!