Granite may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase. It is on this basis that the modern "alphabet" classification schemes are based. The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources). Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks. M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from the mantle. However, this proposal has been rejected by
Granite, Colorado between high, sheer rock outcroppings of buff/pink-colored Precambrian granite. Granite lies at the center of the Colorado Mineral Belt (CMB), a 50 mile-wide strip that runs north and south for 300 miles. Mineralization of the CMB came primarily by way of intrusions of Tertiary Period magmas. The primary ores of the CMB were generally deposited as mixed metal sulfide mineral veins containing pyrite, galena, sphalerite, chalcopyrite, and gold, silver, and copper. During the last glacial period native gold was freed from the host rock and deposited along the ancient roaring Arkansas River bed - much larger than it is today