99 



Auriferous Contact Zones. 



The influence exerted on the Sihui:in strata by the enormous masses of eruptive rooks, sucli as granites, porphy- 

 rites, diorites, felsites, &c., and wliicli now appear as bosses and apophyses, known as dykes, &c. ; and the structural 

 and chemical changes of the mineral components along the planes of the contacts has for sometime been the subject 

 of critical research ; but it was not until the relation Ijetween the occurrence of auriferous quartz veins formed at or 

 near the contacts, both in the eruptive rocks, and to a greater extent in the sediments they invaded, that the 

 attention of practical miners was drawn to the value of following out the contacts in the field as a guide to prospecting 

 operations. In the north-eastern district, in an area hardly yet touched by systematic prospecting, it is estimated 

 that there are fully 300 miles of contact rocks intersected by auriferous quartz veins. 



Maldon. 



The Maldon gold-field is principally to the east of the granitic rocks at Mount Tarrengower. The alteration 

 of the sediments has produced rocks of the hornfels type. A w^ell-defined elvan dyke traverses the field, and in the 

 case of the Derby mine is flanked on either side by auriferous veins. Fully 47 reefs have been described on this field, 

 which strike N. 12 to N. 30 \V. .Several of the "mines are now approaching a depth of 2,000 feet. Such examples of 

 permanency as the South German, &c., may be referred to as illustrating the staljility of mining on the field, which, 

 within a small area, has already produced £2,306,620 worth of gold. 



Stawell. 

 At Stawell the auriferous quartz veins intersect a belt of country margining the granite of the Black Range. 

 The rocks are very much indurated or altered by contact metamorphism, and the sediments are penetrated by 

 numerous dykes of porphyrite and diorite. The auriferous quartz veins strike from south-east to north-west, and 

 generally underlie to westward at an angle of 45 degrees. In almost every instance, except the Magdala-cum- 

 Moonlight, a flat reef has been found alnitting against the vertical on the eastern side, with a northerly underlay, and 



PUDDLING MACHINE. 



the richest quartz has for the most part been found at no great distance eastward from the line of junction. The 

 principal mines include the Magdala, Oriental, Sloane and Scotchman, Perthshire, Hampshire, New Chum, Cross, 

 &c. From this group of mines no less a sum than £4,018,884 worth of gold has been won. A considerable amount 

 of boring has been carried on over this field, and auriferous quartz veins proved in advance of the actual workings. 

 There is no reason why the reefs should not extend still further to the north-north-west of present workings. At 

 present the Magdala, Oriental, and North Magdala are working at a depth of 2,409, 1,832, and 1,640 feet respectively. 



DiORtTE Dykes. 

 In this case the principal bed rock is of Upper Silurian age, and the dykes intersect the strata both with and 

 across the line of strike. The quartz veins traverse the dyke in various ways, either vertically from wall to wall 

 across the dyke parallel to it ; either along the wall or m the body of the stone, and horizontally or nearly so from 

 wall to wall. In places where the dyke stone is absent, the space between the walls is filled with broken-up rubbly 

 shale or slate with thin quartz leaders. Typical examples of such dykes are seen at Wood's Point, Walhalla, Foster, 

 Tanjil, Raspberry Creek, Costerfield, &c, 



