The deposits of the useful minerals & rocks; their origin, form, and content . a knowledge of ore-deposits which they were far from deserving. Chemically, the gold of these lodes is usually substantially purer 1 A7ite, pp. 211, 212. THE OLD GOLD LODES 603 than that of the young gold-silver lodes. As previously stated, these lattercarry gold and silver in variable proportion so that all gradations existbetween gold lodes with little silver and silver lodes with little gold. Inthe case of the group now being described however, the lodes are goldlodes pure and simple. The consequence is that the
The deposits of the useful minerals & rocks; their origin, form, and content . a knowledge of ore-deposits which they were far from deserving. Chemically, the gold of these lodes is usually substantially purer 1 A7ite, pp. 211, 212. THE OLD GOLD LODES 603 than that of the young gold-silver lodes. As previously stated, these lattercarry gold and silver in variable proportion so that all gradations existbetween gold lodes with little silver and silver lodes with little gold. Inthe case of the group now being described however, the lodes are goldlodes pure and simple. The consequence is that the bullion recoveredfrom the young gold-silver lodes usually has a different compositionfrom that of the old lodes ; while with the former there may be 60 percent of gold and 40 per cent of silver, with the latter there is at least 90per cent of gold and at most 10 per cent silver. Concerning primary depth-zones, experience with the old gold lodesappears to have been more favourable than with those of the younggold-silver group. Mining operations have nevertheless shown that a. Fig. 312. -Outcrop of a gold lode witli granite blocks in tlie Lackgruiind, haiuba plateau,German East Africa. Sclieffler. large percentage of the old lodes also have only proved profitable in thecementation zone, the primary ore having been unpayable. Wherehowever the primary ore is rich enough to work, the gold content maycontinue to depths of 1000 m. or more. With these lodes thereforethe ore is more persistent in depth than is the case with the younggold-silver lodes. Finally, mineralogically it is interesting to note that tourmaline ismore often found with the old lodes than with the young, while goldtelluride, w^hich occurs plentifully in some young gold-silver districts, is arare occurrence in the old lodes. As already mentioned, auriferous pyriteis the most common ore-mineral of these lodes, the other sulphides occur-ring subordinately. There are however gold lodes in which the goldis accompanied pa
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