Cu porphyry


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Cu porphyry

  1. 1. Porphyry Copper Deposits
  2. 2. What is a Porphyry? What is a Porphyry Copper Deposit?
  3. 3. Porphyry (por’phy-ry) An igneous rock of any composition that contains conspicuous phenocrysts in a fine-grained groundmass.
  4. 5. Porphyry
  5. 6. Porphyry Copper Deposit A large low- to medium-grade deposit, of primarily of pyrite, chalcopyrite and molybdenite with characteristic concentric zoning of mineralization and alteration around calc-alkaline porphyritic intrusion (typically quartz monzonite to granodiorite)
  6. 7. Typical Grades and Size <ul><li>Copper grade is usually in the range of 0.5 to 1.0%. But can be as high as 1.5 or as low as 0.3%. The lower limit is defined by production costs. </li></ul><ul><li>Zones of local supergene enrichment can contain as much as 20% copper </li></ul><ul><li>Typically 1 to 2 square kilometers in size, but some deposits is in excess of 10 square kilometers. Mineralization has been found to continue to depths exceeding 1km. </li></ul><ul><li>The total amount of ore may be in excess of 3 billion tons (Chuquicamata) </li></ul>
  7. 10. Deposit Tonnage and Grade
  8. 11. Bajo la Alumbrera (Argentina)
  9. 12. Chuquicamata pit approximately 2x4x0.8km
  10. 13. Bingham Pit
  11. 14. La Escondida Chile
  12. 15. Importance of Porphyry CU Deposits <ul><li>Porphyries produce approximately 60% of the worlds copper </li></ul><ul><li>In addition in conjunction with porphyry molybdenum deposits almost all of the world’s molybdenum is produced from porphyry deposits </li></ul><ul><li>Porphyry deposits produce a significant amount of the worlds silver and gold </li></ul>
  13. 16. World’s Leading Copper Producing Mines
  14. 17. World Copper Production/Consumption
  15. 18. Associated Metals <ul><li>Molybdenum </li></ul><ul><li>Gold </li></ul><ul><li>Silver </li></ul><ul><li>Rhenium </li></ul>
  16. 19. Examples of Associated Metal Production <ul><li>In addition to 320,000 tons copper, in the year 2000 Bingham also produced four million ounces of silver and about 500,000 ounces of gold and 21 million pounds of molybdenum </li></ul><ul><li>The Grasberg porphyry mine in Indonesia has an annual production of 1.5 billion pounds of copper and 2.5 million ounces of gold </li></ul><ul><li>Bajo la Alumbrera 2001 production was 674,000 oz of gold and 423 million pounds of copper </li></ul>
  17. 20. Are Porphyry Cu Deposits the Ideal Source for Copper?
  18. 21. Why not Sedimentary Base Metal Deposits?
  19. 22. Why not Sedimentary Base Metal Deposits? Part 2
  20. 23. Global Distribution of Porphyry Cu Deposits
  21. 24. Distribution in Time
  22. 25. Generalized Geology of a Porphyry Cu Deposit
  23. 26. Generalized Geology of a Porphyry Cu Deposit
  24. 27. Proposed Geology of Porphyry Mo Deposit
  25. 28. Geology of the San Manuel Kalamazoo Deposit
  26. 29. Geology of the Chuquicamata Deposit
  27. 30. Geology of the Bajo la Alumbrera
  28. 31. Alteration Zones - Lowell and Guilbert from core of porphyry stock outward <ul><li>Potassic Alteration : Always present. Contains secondary k-feldspar, biotite and/or chlorite, replacing feldspar and plagioclase and mafics. May also contain serecite. </li></ul><ul><li>(Ore Zone) </li></ul><ul><li>Phyllic Zone : Often present. Characterized by vein quartz, sericite, pyrite and lesser amounts of chlorite and illite replacing k-feldspar and biotite. </li></ul><ul><li>Argillic Zone : Sometimes present. Characterized by montmorillonite and kaolinite replacing plagioclase and the replacement of biotite by chlorite. </li></ul><ul><li>Propylitic Zone : Always present and usually has the largest areal extent. Chlorite, calcite and edpidote replacing mafic minerals and to a lesser extent plagioclase. </li></ul>
  29. 32. Alteration and Ore Zoning
  30. 33. Supergene Enrichment
  31. 34. Supergene Enrichment
  32. 35. Fluid Inclusions
  33. 36. More Fluid Inclusions
  34. 37. Fluid Inclusion Findings <ul><li>Fluid inclusion data suggests a two end-member system with mixing </li></ul><ul><li>Magmatic fluid inclusions have very high salinities (30 to 60 wt % NaCl equivalent) and very high homogenization temperatures </li></ul><ul><li>Meteoric fluids have lower salinities (<15 wt % NaCl equivalent) and much lower homogenization temperatures </li></ul>
  35. 38. Fluid Circulation Models
  36. 39. Hydrothermal Alteration
  37. 40. Mineral Stability
  38. 41. Stable Isotope Data
  39. 42. What do Stable Isotopes Suggest <ul><li>Hydrothermal alteration (and most likely metal transport) is the result rock interaction with both magmatic and meteoric water </li></ul><ul><li>Early potassic alteration is most likely the result of rock interaction with magmatic water </li></ul><ul><li>Later quartz-serecite alteration was caused by meteoric water </li></ul>
  40. 43. Mineralization Environment
  41. 44. Radiogenic Isotopes <ul><li>Most Porphyry Cu intrusives often have low 87 Sr/ 86 Sr ratios on the order of 0.703 to 0705 - this is unlike tin and moly porphyries that have much higher Sr ratios. </li></ul><ul><li>Intrusive biotite is usually low in fluorine </li></ul><ul><li>These as well factors as well as the geologic setting point to mantle derived sources for the intrusives - unlike Tin and Moly porphyries which seem to have a much larger crustal component (s-type granites) </li></ul>
  42. 45. Tectonic Controls
  43. 46. Tectonic Control