1. 1. Geological Modelling on the cheap: an example from the Zeehan Ag Pb (Zn Sn) Mining Field Tony Webster
2. 2. Introduction Aim Show: useful geology work can be done with simple CAD software compile & interpret first Especially useful for compiling geo mapping & doing structural interpretation Discuss a few results of a reinterpretation of the geology of the Zeehan Mining Field Done mainly done using CAD Focus is on the historic heart of the mining field NW of the town Emphasis on understanding litho-structural architecture an exploration tool NOT drill-targetting accuracy, at least at first
3. 3. Zeehan Mining Field Late 19th Century Ag-Pb mining field Small, mainly underground mines - independent companies Most productive Ag Pb mines are poorly documented - Little geological information collected in mines - no drilling - No significant exploration since the early 20th Century. Most production prior to 1913. Total production of field: c200,000t Pb, 27,000,000 oz Ag, 2,700t Zn Main historic production from Montana (49,580t Pb, 7,058,122oz Ag) Western (26,300t Pb, 4,800,000oz Ag) Oonah (11,724t Pb, 2,050,135oz Ag) Queen Hill Group (16,532t Pb, 1,973,746oz Ag) Argent Group (4,248t Pb, 561,110oz Ag) Spray (41,700t Pb, 6,456,674oz Ag) Both & Williams, 1968 Frank Long, the discoverer of the Zeehan Mineral Field (Archives Office of Tasmania) Other important mines - not discussed Comstock Spray (fissure vein) Montana Ag Pb Oceana (Limestone-hosted)
4. 4. Generally accepted (published) models The Zeehan orebodies are NNW and NNE striking fissure veins formed along Tabberabberan faults, shears & fractures. Blissett (1962) Metallogenically zoned series of vein deposits developed around the margin of the post-orogenic Heemskirk Granite, and a granite stock below Queen Hill e.g. Twelvetrees and Ward (1910); Both and Rutland (1968); Solomon (1984) Mineralisation ultimately derived from the granite & emplaced in pre-prepared structural sites King and Blissett (1968) recognised a strong association between the best mineralisation & Proterozoic rocks. Solomon (1981) described a possible wall rock influence on the mineral zonation Accepted Models for Zeehan Mineralisation Mineral Zonation Map of Twelvetrees and Ward (1910) Heemskirk Granite Zeehan
5. 5. Zeehans historic mining heart lies in steep rounded hills & linking saddles, dissected by valleys Historic mining landscape Important roads follow mine narrow gauge tramway alignments Key topographic features bear the names of the former mine leases. 2 Km ZeehanQueen Hill Overlaying images Oonah Hill Montana Hill Western Mine Montana Mine Oonah Mine Queen No 4 Many human landscape features remain from the 19th Century Features on modern maps can easily be related to historic maps & plans Overlaying in CAD layers is relatively easy
6. 6. Permian Tillite Unconformity Heemskirk Granite Devonian Bell Shale Florence Quartzite Silurian Austral Creek Siltstone (Sac) Keel Quartzite (Sk) Amber Slate (Sa) Crotty Quartzite (Sc) Ordovician Gordon Limestone (Og) Moina Sandstone (Om) Unconformity Cambrian Crimson Creek Formation (Ecc) Success Creek Group (Esr) Unconformity?? Neoproterozoic Oonah Formation Upper Oonah Fm (quartzite, siltstone, black pyritic carbonaceous shales, vesicular lavas, dolomite & dolomitic shales/siltstones) Variably schistose quartzite and siliceous siltstones Regional Geology Extract: !:50,000 Geological Map of the Zeehan Region (Brown et al, 1986). 5 Km ZEEHAN N Heemskirk Granite
7. 7. Heemskirk Granite The granitoids of western Tasmania are: Essentially post-kinematic Dated to 335-370 Ma (Devonian) Locally aligned parallel to the regional grain Solomon and Groves (2000) Regional Geology Heemskirk Granite An apophysis of Heemskirk Granite has been interpreted to lie approx 1km below Queen Hill (Solomon, Leaman) 5 Km N Compiled & dissected in CorelDraw
8. 8. Heemskirk Granite Regional Geology Oonah Formation 5 Km Lower Neoproterozoic, 1000750 Ma Depositional age constrained by: youngest detrital zircons in the sequence (1070 Ma) and c.750 Ma age of the overlying Success Creek Group Seymour et al (2007) N Distinctly different Upper Oonah Fm is host to most mineralisation in the Central Zeehan Field. Comprised of quartzite (often micaceous), siltstone, black pyritic carbonaceous shales, vesicular lavas, dolomite & dolomitic shales / siltstones) Seymour et al (2007) Variably schistose quartzite and siliceous siltstones Compiled & dissected in CorelDraw
9. 9. 5 Km Heemskirk Granite Regional Geology - Upper Oonah Formation N Limestone Micaceous Quartzite Black Shale (pyritic) Volcanics (spillite) Bedding form surfaces Faults Early fold trends blue dotted lines Later fold trends (and faults) - red Compiled & dissected in CorelDraw
10. 10. Gordon Limestone Moina Sandstone Crotty Quartzite Florence Quartzite 5 Km Permian Tillite Unconformity Heemskirk Granite Devonian Bell Shale Florence Quartzite Silurian Austral Creek Siltstone (Sac) Keel Quartzite (Sk) Amber Slate (Sa) Crotty Quartzite (Sc) Ordovician Gordon Limestone (Og) Moina Sandstone (Om) Unconformity Cambrian Mt Zeehan Conglomerate Crimson Creek Formation (Ecc) Success Creek Group (Esr) Unconformity?? Neoproterozoic Oonah Formation Upper Oonah Fm (quartzite, siltstone, black pyritic carbonaceous shales, vesicular lavas, dolomite & dolomitic shales/siltstones) Variably schistose quartzite and siliceous siltstones Regional Geology Younger Strata N Compiled & dissected in CorelDraw
11. 11. Regional Geology Silver Lead Mineralisation Gordon Limestone Moina Sandstone Crotty Quartzite 5 Km Florence Quartzite Stratabound Mineralisation Structurally-hosted Mineralisation Heemskirk Granite N Compiled & dissected in CorelDraw Min focussed in regions of high structural complexity - particularly in the upper Oonah Formation
12. 12. Mine Geology Geological Interpretation Oonah Mine No 4 level Based on survey plans and written descriptions Compiled in CorelDraw
13. 13. Mine Geology Geological interps of all Oonah Mine levels (stacked level plans) Compiled as separate layers in CoreDraw Can scroll through interpretation layers - like using a light table Twelvetrees & Ward 1912Compiled in CorelDraw
14. 14. Oonah Queen Group Mine Compilation Red lines = lodes Blue lines = faults Mine Geology to Mining Field Geology Compiled in CorelDraw Montana & Montana No 2 Western Oonah
15. 15. Oonah Queen Group Mine Compilation Surface Geology and structural interpretation Based on detailed mapping from various sources (mainly RGC Exploration). Red lines = lodes Blue lines = faults Green = Volcanics in Oonah Fm Blue = Quartzite Mine Geology to Mining Field Geology Compiled in CorelDraw
16. 16. Getting it into 3D when the time comes A CAD layer with registration points can be exported with any other layer in the project . The same reference points can be used to register each exported image in the 3D or GIS packages
17. 17. Getting it into 3D when the time comes 3D topo model of central Zeehan field with registered image of CAD geology interp maps Micaceous Quartzite Black Shale (pyritic) Volcanics (spillite) Bedding form surfaces Faults
18. 18. Mine Geology - 3D 3D model of the Oonah Mine workings & geology Lodes & other mineralisation Faults Volcanic contacts at surface Workings Twelvetrees & Ward 1912 NORTHWEST
19. 19. Mining Field Geology - 3D Micaceous Quartzite Black Shale (pyritic) Volcanics (spillite) Bedding form surfaces Faults Relationship between deposits and stratigraphy SE plunge southeast
20. 20. Volcanic contacts at surface Workings Mining Field Geology - 3D Relationship between deposits and stratigraphy SE plunge southeast Oonah Mine Western Mine Montana No 2 Mine Queen No 4 Workings
21. 21. Lodes & other mineralisation Volcanic contacts at surface Workings Mining Field Geology - 3D Relationship between deposits and stratigraphy SE plunge southeast Oonah Mine Western Mine Montana No 2 Mine Queen No 4 Workings
22. 22. Lodes & other mineralisation Volcanic contacts at surface Mining Field Geology - 3D southeast Oonah Mine Western Mine Montana No 2 Mine Queen No 4 Workings Relationship between deposits and stratigraphy SE plunge
23. 23. Most mineralisation in central Zeehan field is stratabound -The mineralisation is located at or near the contacts of the volcanics and black shales Mineralised stratabound horizons are dislocated by NW-SE- trending faults - NW-SE Faults are largely un-mineralised (note: not the case for the Spray Mine). Most lodes dip to the SE, parallel to the plunge of folds in the cover stratigraphy (refolding of Oonah Fm basement) - There is a probable spatial association with SE plunging fold hinges in the Oonah Fm A simple zoned mineral field model does not stand up to close scrutiny - stratigraphy, lithology are key influences on the distribution of mineralisation Some Results Spray Mine Main Shaft. Mineral Resources TasmaniaThe Upper Oonah Fm is the most important control on ore localisation It is the key exploration target
24. 24. Severn Sn Mineralisation Queen Hill Sn Mineralisation Montana Sn Mineralisation Recent work by Stellar Resources - an apparent Pb to Sn zonation Tim Callaghan Is it any use?
25. 25. If the Stellar Resources interpretation is correct, do all of the Zeehan stratabound Ag Pb lodes (e.g. Western & Montana) persist down-plunge to the SE and become more tin-rich? Sn? Sn? Sn? Lodes & other mineralisation Volcanic contacts at surface Severn Sn Queen Hill Sn Montana Sn Western Ag Pb Montana Ag Pb Oonah Ag Pb + stannite southeast Is it any use?
26. 26. Acknowledgements CODES MRT TIGER system MRT Library (Kylie Lau & Greg Dickens) MRT Data Management (Ken Bird)