At Sams Creek a gold-bearing, peralkaline granite pophyry dike intrudes
Ordovician-Silurian metapelite and quartzite. These metasedimentary rocks have
undergone three phases of folding: a first phase of recumbent folds (F1), a
second phase (F2) of northerly-trending inclined folds with a prominent
crenulation cleavage, and a third phase (F3) of steeply plunging folds. The
granite porphyry dike has a thickness of up to 40 m and intrudes thin
lamprophyre dikes along its contacts. Deflection of the crenulation cleavage
around the granite dike, shearing within the dike and its sinuous outcrop
pattern indicate that the granite dike has been deformed during F2 and F3. The
granite has been hydrothermally altered, with a first stage of
magnetite-ankerite alteration. This first stage is cut by a second stage of
quartz-pyrite veins and a third stage of sulphide, quartz and ankerite veins,
accompanied by pervasive silicification represented by
quartz-perthite-albite-rutilepyrite-ankerite-sericite assemblages. Lamprophyre
is altered to an ankerite-chlorite-sericite assemblage. The sulphide veins are
composed of arsenopyrite + pyrite gold galena sphalerite chalcopyrite
pyrrhotite. The altered granite and the veins have been deformed and
recrystallised. The competent sulphide minerals pyrite and arsenopyrite are
fractured and brecciated, with fractures locally filled by galena, a ductile
sulphide mineral. Vein quartz shows local cataclastic and mortar textures and
develops pressure shadows around arsenopyrite. Alteration and mineralisation are
confined to the granite porphyry and adjacent lamprophyre. These features
together with the style of veining and the sulphide mineralogy indicate that the
mineralisation was formed from a magmatichydrothermal fluid that was sourced
from the granite. Oxygen, carbon and sulphur isotope values of the vein minerals
(quartz, ankerite and sulphides) are also consistent with a magmatic
source.