Quartz vein systems at the San Antonio mine are hosted almost exclusively by the SAM unit.
Generally veins terminate at its contacts, or extend a few meters into surrounding felsic
volcanic rocks with rapid decrease in vein width and continuity, gold grade, and associated
extension veining. Mineralization is best, or exclusively developed in the upper,
leucogabbro portion of the SAM unit, and does not generally extend into melagabbro that
forms the base of the unit.
Composite plans showing vein distribution, type and relationships to SAM unit thickness
throughout the deposit are in Figures 4 to 6 and representative level plans are in Figures 9-
11. The distribution of vein systems defines a northeast plunging mineralized zone within
the SAM unit that is 1000-2000 feet wide and has been traced from surface to the lowest
depths of the mine over a down plunge distance of 7000 feet (vertical distance 5000 feet).
Vein systems are most abundant and best developed where the SAM unit is 200-400 feet
thick in an area immediately north-northwest of the generally northeast plunging axis defined
by the thickest (500-600 foot) part of the SAM unit (Figure 4). To the north of this area, the
gabbro thins to less than 100 feet thick, and vein abundance rapidly diminishes. A gap that
occurs between 22 and 28 levels where vein abundance is markedly lower than in
surrounding areas, corresponds with a thin section in the axis of the widest portion of the
SAM unit, in which the SAM unit is less than 400 feet thick (Figure 4). The current area of
mining is exploiting veins over a strike length of approximately 1000 feet, which is
significantly shorter than strike lengths developed in upper portions of the mine, and slightly
east of the down plunge projection of the system on higher levels. The shorter strike length
may reflect a primary change in the structural style of the system, but is also in part an
artifact of the current area of underground development; the step to the east is probably a
function of the thickness of the SAM unit.
