GEOLOGIC AND ECONOMIC BACKGROUND 47 



B. VEINS, LODES, AND DIKES (REGULAR DEPOSITS) 



1. Lodes in which the valuable ore mineral has diagnostic physical properties, e.g., 

 sulphide ore bodies having high electrical conductivity 



2. Lodes in which the valuable ore minerals are genetically and structurally asso- 

 ciated with minerals having diagnostic physical properties, e.g., auriferous pyrite 

 veins containing electrically conductive pyrite 



3. Gold-quartz veins 



4. Pegmatite dikes 



5. Lodes in which the ore mineral is a refractory type (non-magnetic, non- 

 conductive, etc.), e.g., sphalerite veins 



C. IRREGULAR CONCENTRATED DEPOSITS 



1. Shear zones 



2. Pipes and stocks 



3. Replacement deposits 



4. Contact-metamorphic deposits 



5. Magmatic segregations 



D. DISSEMINATED DEPOSITS 



1. Disseminations in igneous rocks, e.g., "porphyry coppers" 



2. Disseminations in sedimentary rocks 



E. BEDDED DEPOSITS 



Metallic 



1. Gold-bearing conglomerates (South African) 



2. Sedimentary iron ores 



3. Residual deposits 



4. Copper-bearing conglomerates and lavas 



Non-Metallic 



1. Sedimentary rocks 



2. Saline residues 



3. Residual deposits 



4. Coal and lignite 



5. Miscellaneous non-metallic deposits 



However, in determining the applicability of geophysical methods, the 

 form, size, and mineralogical content of an ore body are usually more 

 important than its genesis. Table 4, while incomplete from a genetic 

 viewpoint, illustrates all the common forms of ore or mineral deposits 

 which normally need be considered in studying the applicability of geo- 

 physical methods. 



Placer Deposits 



Geophysical methods have been extensively and successfully employed 

 in placer exploration, t Gold placers are the best known of this type of 



t A. Gibson, "Magnetometric Determinations Applied to Placer Mining," Ens. and Min. Jnl. 

 (1922), vol. 114. 



K. C. Laylander, "Magnetometric Surveying as an Aid in Exploring Placer Ground," Em. 

 and Min. Jnl. (1926), vol. 121. 



C. A. Heiland and W. H. Courtier, "Magnetometric Investigations of Gold Placer Deposits 

 near Golden, Colorado." A.I.M.E. Geophysical Prospecting (1929.) 



Dart Wantland, "Comparison of (5eophysical Surveys and the Results of Operations at the 

 Roscoe Placer of the Humphreys Gold Corporation, Jefferson County, Colorado," Colorado School 

 of Mines Quarterly, Vol. .32, No. 1, January, 1937, pp. 87-118. 



H. R. Joesting, "Magnetometer and Direct Current Resistivity Studies in Alaska," A.I.M.E. 

 Tech. Paper 1284, February, 1941. 



