B066: Interpretation of leached outcrops |
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Roland Blanchard, Augustus Locke and several others were pioneers in the 1930s in figuring out the geology and significance of leached capping and gossans and their application of finding underlying ore deposits. Several others carried on this work, some of whom were mentors to this reviewer. Those included E.N. Pennybacker, Kenyon Richard, Harold Courtright, Ray Ludden, Bob Ludden, Ray Robinson, Larry Beale and others. Discoveries or extensions made with careful mapping and capping studies included Quellaveco, Toquepala, Silver Bell, La Caridad and many of the 1950s and 60s Arizona porphyries. The advent of IP-resistivity and other geophysical methods sort of shoved this discipline aside. However the color photos in Blanchard's work should be studied by every exploration geologist in every terrane. There is nothing like boots on the ground for finding ores. Andrew E. Nevin, March 24 2012
Contents
༢ Boxwork derived from chalcopyrite 2 Oxidation products of an arsenopyritepyrite mixture | 2 |
Coarse and fine cellular boxwork derived from chalcopyrite | 4 |
Finely cellular boxwork derived from chalcopyrite | 5 |
Goethite boxwork derived from chalcopyrite | 6 |
Limonite formed by weathering of a chalcopyritepyrite vein | 7 |
Oxidation products of a disseminated chalcocitepyrite mixture | 8 |
Cellular limonite formed from a mixture of chalcocite and pyrite | 9 |
Cellular and fluffy limonites from Bagdad Ariz | 10 |
Chapter 10Limonite precipitation related to oxidation of ironfree sulfides | 57 |
Chapter 12Limonite precipitation by reaction with neutralizing gangues | 65 |
Longitudinal section of Great Cobar mine New South Wales | 70 |
Sections of workings at Mount Isa mine Queensland | 73 |
Sections of workings at Mount Stewart mine New South Wales | 75 |
Chapter 14Influence of the sulfuriron ratio and the host rock on | 81 |
Sketch showing cellular pseudomorphs and other limonite prod ucts formed at the Republic mine Ariz | 86 |
Chapter 15Limonite color | 89 |
Chapter 3Indigenous fringing and exotic limonites | 11 |
Cleavage boxwork formed from oxidized galena | 12 |
Oxidation products of galena in limestone gangue | 13 |
Relief limonite derived from galena | 14 |
Hieroglyphic boxwork derived from sphalerite | 15 |
Cellular boxwork derived from sphalerite | 16 |
Limonite formed by leaching of smithsonite | 17 |
Leaching products of pyritechalcopyritesphalerite mineralization | 18 |
Chromitederived honeycomb boxwork and cellular sponge | 19 |
Alteration of magnetite to hematite and then to goethite | 20 |
I Cellular pseudomorphs | 21 |
Leaching products of crystalline fluorite in a galenamarmatite orebody | 22 |
II Massive jasper | 29 |
A B Typical specimens of Australian Billy | 37 |
Chapter 7Extent of limonite precipitation above and below the water table | 41 |
Chapter 9Limonite precipitation through dilution of ironbearing solutions | 51 |
Chapter 17Examples indicating the value of leached outcrop interpretation | 109 |
Map showing a method commonly used in classifying leached outcrops over disseminated copper deposits | 110 |
Section showing how leached material found only underground led to discovery of an important orebody | 111 |
Part 2 | 113 |
Sketch showing precipitation of pyritederived limonite at lime stone contact | 115 |
Sketches of typical oxidation products of pryrite in three types of gangue | 116 |
Oxidation products of pyrite in slightly and well kaolinized quartz monzonite | 117 |
Chapter 19Pyrrhotite | 122 |
Chapter 21Chalcopyrite | 132 |
Chapter 23Bornite | 138 |
Oxidized copper minerals | 144 |
Summary | 154 |
Chapter 28Molybdenite | 160 |
Chapter 32Calcite | 166 |
Chapter 36Supergene silica | 172 |
Common terms and phrases
acid amount appearance attack Australia become Blanchard body bornite carbonate carried cavity cell cellular boxwork chalcocite chalcopyrite chapter characteristic closely coated color complete composition containing copper crusts deposits depth derived developed disseminated districts effect Enlargement especially example exist exotic extent feet ferric oxide field FIGURE formation fracture fringing galena gangue given goethite grade grains granular ground water hypogene inch indigenous iron leached leached outcrop lead less limestone limonite derived limonitic jasper mass massive material minerals Mining mixture moderate mole nature nearly neutralizing power observed occurs orebodies origin outcrop particles pattern percent portion precipitated present pyrite pyrrhotite quartz rarely ratio reactions regions remains replacement represented result rock sericite shale showing shown silica solution specimen sphalerite sponge strongly structure sulfate sulfide sulfur supergene surface thickness tion usually walls water table weathering yield zone