B066: Interpretation of leached outcrops

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NV Bureau of Mines & Geology
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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

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