Tin and tungsten veins and skarns in the McQuesten River area occur in the contact zones of Cretaceous feldpspar-porphyritic biotite granite stocks, plugs, and dykes. Most occurrences are located in the exocontact of plutons, in the brittle metasedimentary country rocks known as the Grit Unit of Upper Precambrian to Lower Cambrian age. Cassiterite (+/- silver) occurs in chlorite-, tourmaline-, and quartz-matrix breccias with fragments of quartzite, schist, and vein material of chlorite, tourmaline or quartz; in thin veinlets with little gangue of tourmaline, K-feldspar, or muscovite; and in actinolite-quartz-epidote-axinite-garnet skarn (+/- pyrrhotite, pyrite and chalcopyrite).
Scheelite is mainly disseminated in fine-grained, diopside-quartz, or actinolite-quartz (+/- pyrrhotite) exoskarn which is interlayered with white wollastonite-quartz skarn. Scheelite (+/- molybdenite) also occurs in sheeted quartz (+/- feldspar) veins in both the endo- and exocontact regions of two feldspar-porphyritic granite stocks. Rarely do tin and tungsten occur together, however some low tin values are found in some tungsten occurrences, and vice versa. Tungsten occurs closer to the associated intrusion than tin.
