Download STAGE I – Formation of Multiple Ore Deposits

Modified from various sources – see references.
STAGE I – Formation of Multiple Ore Deposits
The KSM and Pretium deposits were born in what is known as an island arc environment about 190 million years ago. Arc magmas are derived from
partial melting of hydrated rocks which have been drawn down to higher pressure and temperature conditions during subductive tectonic plate
collisions. The relatively buoyant magmas rise up along faults, dissolving and concentrating metals and sulfur in hydrous fluids and gases. The pressurized,
metal rich fluids and gases circulate through the solidifying magma and host rocks, depositing metals and altering minerals, producing the typical
“porphyry” zonation patterns seen in KSM’s deposits which reflect hotter conditions in the center transitioning outward to cooler surroundings. If the
magma approaches or breaches the surface, as at KSM, the lower pressure and temperature conditions and the presence of ground water may result
in epithermal gold-silver deposits—either low grade disseminated ones or high grade vein deposits such as Brucejack and the Camp zone. *For references, see page 1.
STAGE II – Compression, Thrust Faulting, Erosion
The period of ore deposit formation is relatively short, and eventually tectonic conditions change, and the systems are either eroded away, or, as in the
case of KSM, are buried and preserved by volcanic and sedimentary rocks. During this period, the tectonic plate hosting KSM was forced northward,
fragmented and squeezed or compressed against the older and ridged North American plate. In northwestern British Columbia, the compressive
processes resulted in folding and thrust faulting which pushed deeper, older rocks above younger rocks. These mountain building episodes uplift whole
regions and promote erosion.
Stage III – Extension, Normal Faulting, Erosion
Tectonic processes are dynamic and, over time, compressive conditions often reverse to extensional conditions where plates are drawn apart
by opposing forces. This is typically accommodated by development of normal faults and grabens which allow the plate to “stretch out”. The
deformational history at KSM has resulted in a rearrangement of the original pattern of deposits; the initial order of deeper, porphyry-style, stockwork and
vein controlled gold-copper mineralization transitioning upward into epithermal style, vein and disseminated gold mineralization is now reversed. This
complicated geological architecture has dramatic consequences for exploration targeting. The presence of undiscovered, “blind” deposits beneath
faults in other mining districts with multiple magma sources and deformational histories similar to KSM, such as Oyu Tolgoi, Pebble, Resolution, and
Grasberg, demonstrates the sizeable potential rewards open to a flexible and persistent exploration strategy. In 2013, Seabridge plans to drill several
promising targets which have characteristics of high grade core zones (see Exploration Programs on page 5).