446 Transactions.—Geology. 
several classes, and in an alluvial form, it being from the alluvial workings 
that by far the greater quantity of gold has been obtained. The goldfields 
have been divided on the Geological Map into Northern, Central, Western, 
and Southern, and the gold from the different localities varies considerably in 
purity. That from Otago or the Southern fields and from Westland is pure 
or nearly so, being alloyed with less than 6 per cent. Ag., and alittle copper. 
In Nelson it is alloyed with 10 to 14 per cent. of silver, while at the Thames 
or Northern goldfield it is generally alloyed with over 30 per cent. of silver, 
thus corresponding in composition to the Electrum* of Klaproth, which con- 
tains gold 64, and silver 86 per cent. There is also a marked difference in 
the associated minerals north and south, which, of course, is dependent upon 
the rocks from which the gold is derived. Thus in the Southern goldfield 
it is associated with Platinum, Zircons, and Garnets, as well as Black Hema- 
tite and Scheelite; in Nelson it occurs with the rare minerals Osmiridium 
and Platiniridium, and in the Northern goldfields Native Arsenic, Copper 
Pyrites, Galena, Zine Blende, and Stibnite occur in the reefs, these being 
also more or less represented at Collingwood and at parts of the West 
Coast. The different characters of the reefs and mode of deposition are, 
however, the most marked and interesting in different localities. 
In the Southern goldfield at Macetown and Cromwell these reefs are of 
a truly brecciated character (Hector, Geol. Rep. 1878-9, p. 24), being com- 
posed of angular fragments of slate and schist cemented by quartz, with 
which gold has been infiltrated in a very pure form. The gold in these 
reefs must have been introduced by mechanical means, but some has prob- 
ably also been deposited from solution; but these reefs which occur im 
metamorphic schists have probably been formed subsequently to those in 
the foliated schistose rocks and slates, which belong to the next group, 
and from which they have derived their gold to a large extent. The reefs 
of the Reefton district, on the other hand, are true fissure reefs, and owe 
their origin to fractures produced by contortion, those which occupy the 
synclines widening as they descend, while those on the anticlines die out 
in depth or come to be nothing more than strings. Outliers of the same 
formation of reef oecur at Cardrona. These fissures having been formed by 
the same action which induces cleavage elsewhere, during the plication of 
the strata on a large scale, have given rise to subterranean channels, 7 
which the quartz and gold have been deposited from solution. The reefs 
thus formed consist of solid, compact quartz, and correspond more to the 
Australian reefs than any others. It is hard to assign any reason for the 
precipitation of gold in cases of this sort, and a field of hye’ 
open for anyone who feels disposed to take it up. : WG 
* Hector “Trans. NZ. Inst,” vol i.,p-366000 es a 
