The deposits of the useful minerals & rocks; their origin, form, and content . quartz1 Ante, pp. 247, 288, II F 580 ORE-DEPOSITS as the principal gangue - mineral. Fluorite, zeolites, carbonates, andbarite are absent from most, though the two last-named appear abundantlyin some. With these lodes also, gold and silver are closely associated,these two metals either occurring together in the same lode or in separatethough neighbouring lodes. For instance, in the important silver districtof Hualgayoc the gold is practically limited to one single lode. Humboldt ^estimated the average annua
The deposits of the useful minerals & rocks; their origin, form, and content . quartz1 Ante, pp. 247, 288, II F 580 ORE-DEPOSITS as the principal gangue - mineral. Fluorite, zeolites, carbonates, andbarite are absent from most, though the two last-named appear abundantlyin some. With these lodes also, gold and silver are closely associated,these two metals either occurring together in the same lode or in separatethough neighbouring lodes. For instance, in the important silver districtof Hualgayoc the gold is practically limited to one single lode. Humboldt ^estimated the average annual precious-metal production of Potosi up tothe coinmencement of the nineteenth century at 481,830 marks ^ of silverand 2200 marks of gold, or 1 part of gold to 200-250 parts of silver. Many of the lodes are characterized by well-defined primary depth-zones. Those of Cerro de Pasco- for instance, which in times past wereresponsible for the greatest silver j)roduction of Peru and for centurieswere worked almost exclusively for silver, in depth passed over in part to Fig. 309.—Diagrammatic section across Cerro de Potosi, showing the collection of lodes atthe contact of the eruptive with the sediments, and the diminution of the number of lodes in dotted lines represent the beds removed by erosion. Steininann, 1910. become copper lodes. In the case of the silver-tin lodes of Bolivia, thetin according to Steinmann is generally fomid concentrated in the upperlevels, while the silver ore is found below. Many of the silver lodesproper contained quantities of secondary silver minerals in the oxidationzone, such for instance as native silver and cerargyrite, which are easilyamalgamable ; it is nevertheless a striking fact that secondary enrichmentsuch as constitute a cementation zone is, according to Steinmann,either entirely absent or extremely infrequent. The silver-tin deposits of Bolivia, which have been more particularlyinvestigated by Stelzner, are of es
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectminesandmineralresou
