Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/360

 " The tin crystals are principally associated with the quartz in the most highly micaceous portions."

And, speaking of the alluvial drifts from these stanniferous granites, he adds : —

" Their richness and continuousness is extraordinary, and, I should think, quite unparalleled in any other country."

In the metamorphic system, indeed, is the most varied development of metallic ores in Queensland ; in it also the greatest number of " true lodes " have been found ; and this fact affords the best reason for the supposition that the comparatively unexplored districts at the heads of the Mitchell and in the McKinlay ranges, where large tracts of metamorphic rocks are known to exist, will yet add very much to the mineral exports of Queensland when thoroughly prospected. From the exploring expedition about to start into the former of these districts great results may be expected.

Granitic.

Outcrops of granite extend along the eastern coast of Queensland from Cape York nearly up to Broadsound, and inland as far as the heads of streams running direct from the inner coast range to the sea. Isolated patches of the same character of rock are found at intervals from the seaboard back to the coast range, going south from Broadsand.

Very little rock of this character is met with west and south of the dividing range which separates rivers flowing to the eastern and northern coast and those trending south to the Murray or Coopers' Creek.

In their lithological character, the granites of Queensland vary very much in their crystalline texture and arrangement of minerals in the same rock-masses, passing from true granites into porphyry and quartz-porphyry; but the monoclinic felspar is always in excess of the triclinic.

With the exception of molybden-glance, found in the porphyry near Townsville, no metallic ores are associated with the granites proper.

Trappean.

In a previous portion of this paper much stress has been laid on the value of certain intrusive Trap-rocks as specially influencing the production of auriferous veinstones in Queensland ; and it is now proposed to investigate this subject somewhat more in detail.

The petrology of these may be divided into four type classes : —

1. Pyritous porphyrites and porphyries.

2. Pyritous diorites and diabases.

3. Chrome-iron serpentines.

4. Pyritous felsites.

Group 1.

The analysis of a characteristic specimen of a porphyrite of Group 1 (Pl. XI. fig. 2) gave the following results : —