Alteration_Mass_Balance

Wednesday 15 august 12 from large and mcgoldrick 1998

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Unformatted text preview: ednesday, 15 August, 12 Hellyer VHMS Alteration Zonation From Gemmell and Fulton (2001) and Large et al. (2001a) Wednesday, 15 August, 12 Alteration Indexes: Examples • SEDEX AI = 100*(FeO+10MnO)/(FeO+10MnO+MgO) [Large + McGoldrick (1998)] • Based primarily on the increase in FeO and MnO at the expense of MgO during the alteration of dolomitic sedimentary rocks. Wednesday, 15 August, 12 From Large and McGoldrick (1998) Wednesday, 15 August, 12 Alteration Indexes: Examples • SEDEX Metal Index = Zn+100Pb+100Tl [Large + McGoldrick (1998)] • This is based on simply on the the increase of these metals proximal to ore in the SEDEX systems in Mt. Isa block. Wednesday, 15 August, 12 From Large and McGoldrick (1998) Wednesday, 15 August, 12 Alteration Indexes: Examples • ! Au Indexes: CO2/Ca, K/Al, 3Na/Al, 1000Y/Tidepletion [Eilu et al. (2001)] • Based on : • CO2/Ca – based on increase in CO2 during carbonate alteration. • K/Al, 3Na/Al – assuming Al conserved, K and Na increases during sericite-phengite-carbonate alteration. • 1000Y/Tidepletion – Y increases, Ti depletes proximal to ore Wednesday, 15 August, 12 From Eilu et al. (2001) Wednesday, 15 August, 12 From Eilu et al. (2001) Wednesday, 15 August, 12 +Sr, Ca, Tl, Ba, Co, Pb, As, Fe, Mg, Zn, Cu, Si ORE Wednesday, 15 August, 12 -Na, Rb, La, Ce, Eu +Sr, Ca,Tl,Ba,Co,Pb, As -Na, Rb Alteration Indexes: Examples • Hypothetical Index: • Want to weight data proximal versus distal to ore. • • • Weight proximal gained elements more than distal elements. Weight proximal lost elements in more negative fashion than distal – will increase index ratio. Since ppm and weight percent we must normalize: • • • • Wednesday, 15 August, 12 Z-score of analytical data 2σ error on analytical data Some reservoir (PM, CC, etc.) Log transform data and then standardize. Alteration Indexes: Examples • Hypothetical Index: • n - weighting factor – weighted greater because proximal to ore (n>1). • m – weighting factor – weighted less because in bottom of equation and we use a lower number it will increase the HI value (m<1). Wednesday, 15 August, 12 Spatial Data Analysis: Integrating GIS and Downhole Profiles for Vectoring in Exploration • While the previous indicates how to identify the evidence of alteration, a key is utilizing these data to target areas for exploration. • On regional to property scale, the key is utilizing GIS software (e.g., ArcGIS and Mapinfo) to view data in space via contour plots and bubble plots. • On deposit scale and/or when drilling the key is visualization of downhole chemical profiles and 3D shells of geochemistry using standard spreadsheet software and 3D GIS software (e.g., ER Mapper, Geosoft Target). • GIS also allows integration and correlation of other types of data (e.g., geology, geophysics, surficial geology, etc.). Wednesday, 15 August, 12 Wednesday, 15 August, 12 Project X: Na2O Alteration Contours Wednesday, 15 August, 12 Project X: K2O Alteration Contours Wednesday, 15 August, 12 Downhole Profiles • Requires detailed sampling downhole every 20-25 meters (e.g., every 4-5 boxes), whenever there is a change in lithology, or when there is a change in alteration mineralogy or alteration intensity. • 300 meter hole ~$100-200K drilling (more in remote locations like arctic); ~20 litho samples at $100/ sample = $2000 - THIS IS PALTRY IN COMPARISON TO THE COST OF DRILLING AND THE INFORMATION YOU CAN GET FROM THE DATA. • You get downhole profiles for elements and element ratios that can be utilized to tell you: • • • • Are we in the right ball park? Should we extend a drill hole? Which direction should we be drilling next? We then have 3D lithogeochemical cubes that we can use to vector. Wednesday, 15 August, 12 6 1000200030004000 102030405060708090 20 30 40 50 60 70 80 90 100 200 300 400 500 24 41 56 69 90 110 130 150 169 189 204 219 235 249 279 294 310 324 338 360 380 400 428 449 468 490 515 554 579 599 Wednesday, 15 August, 12 10 20 30 40 500 1000 Ba/Sr 10000 30000 50000 20000 40000 60000 MgO/Na2O 5000 1000015000 K2O/Na2O Spitz 5 CCPI 4 AI 3 Pb 2 Zn 1 Cu Na2O FROM Deposit X: Downhole Profile 500 1000 Al2O3/Na2O> 2.5% Cu > 2.5% Wednesday, 15 August, 12 Summary • • Element mobility. • Methods of calculating mass and elemental change during hydrothermal alteration. Philosophical approach to sampling and setting up the alteration problems. • • • • MacLean, Stanley, Element Ratios, etc. Other tools in alteration geochemistry. Alteration indexes: examples and construction of your own. GIS and 3D Visualization of data on surface and in drill core. Wednesday, 15 August, 12...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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