388 SECTIONAL TRANSACTIONS.—C. 
Mutual benefit follows from this closer association of ‘the two subjects. The 
mining geologist, on the one hand, is guided by the important principles established 
by petrologists in relation, for example, to magnetic differentiation, and the 
assimilation of adjacent rocks to which Dr. Brammall has to-day made a notable 
contribution ; and petrologists, on the other hand, will not be content to base their 
conclusions as to rock formation on minerals that are transparent in thin section, 
but will pay more attention than formerly to the significant presence of opaque 
minerals, especially now that modern technique enables even small disseminated 
grains of these latter minerals to be determined as separate species. 
There is some satisfaction in knowing that petrologists are confirming that 
experienced mining geologists have been pursuing their subject on right lines. The 
intimate genetic relationship between certain ore-deposits and the containing or 
neighbouring igneous rocks, has long been established, and forms one of the main 
principles that have guided the mining geologist in his search for new deposits, and in 
the study of mineralized areas. 
The recognition of the genetic relationship of igneous rocks over considerable 
areas, as in petrographic provinces, has enabled petrologists to form conclusions 
of the greatest importance. Similarly, the recognition of the genetic relationship 
of ore-minerals in metallographic provinces, enable mining geologists to advance 
conclusions of great economic importance. Again, the differences observable in 
certain related igneous rocks have been shown by petrologists to be due mainly to 
differences in the temperature and pressure conditions under which they con- 
solidated ; these same factors have been shown by mining geologists to account, in 
great measure, for the variations in mineral deposits of primary origin, when followed 
in depth or in a lateral direction. 
This brings me to the point I should like to emphasize, namely, that mineralizing 
processes related to igneous rocks are best understood, not mainly from the examina- 
tion of specimens under the microscope, or on evidence from one part of a mineralized 
area, but from the study of the mineralization in relation to the metallographic 
province in which it occurs, paying particular attention to the zonal arrangements 
of the minerals. Consequent on changes subsequent to the primary mineralization, 
parts of a mineralized area may show evidence that can be very misleading. It is 
my opinion that certain hypotheses, now discredited, on the genesis of mineral 
deposits would not have been advanced if the mineralization had been considered on 
these broader lines ; for although the workable parts of a deposit may be very con- 
fined, yet the mineralization in the scientific sense is often as widespread as are the 
related igneous rocks. This is a fact of great significance, and I am convinced that, 
in some cases, disseminated grains of ore-minerals can furnish as reliable evidence of 
the genetic relationship of separated outcrops of igneous rocks as do rock-forming 
minerals, for both groups of minerals are often of common parentage. The Cornish 
granite masses, for example, are to some extent stanniferous; the cassiterite is 
genetically intimately related to the granite and granitic rocks, and its presence appears 
to me to be as helpful an indication of the common parentage of the various granite 
masses aS any other mineral common to them. The general predominance of 
woltramite over cassiterite in parts of Lower Burma; the predominance of cassiterite 
over the tungsten mineral in Malaya and the Dutch East Indies; the occurrence of 
these two minerals in closer proportions at intermediate places ; and the fact that the 
tin and tungsten minerals are present to some extent in innumerable areas where 
granite and granitic rocks occur in the belt stretching for hundreds of miles from 
Lower Burma to Siam, Malaya, and the Dutch East Indies, lead to conclusions of 
great scientific and economic importance.! It is no coincidence, but the result of 
differences of relative temperatures of formation of the tin and tungsten minerals, 
that in the wolframite-cassiterite zone the metamorphosed sedimentaries have a 
general lower cassiterite ratio to wolframite than in the granitic rocks, and that there 
is a general predominance of the tungsten mineral in the northern and less denuded 
part of this metallogenetic province. It is not surprising, when these mineralized 
areas are considered as parts of the same metallographic province, to find striking 
similarities in the granites and granitic rocks from Lower Burma southwards to the 
Dutch East Indies, and in the metalliferous minerals they contain. 
' Jones, W. R.: ‘Tin and Tungsten Deposits: their relative temperatures of 
formation.’ J'rans. Inst.M.M. 1919-1920, pp. 320-376. 
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