The St. Francois Mountains igneous complex of Proterozoic age consists of hypabyssal, granite plutions intruded into the overlying rhyolites of similar age. Melting and crystallization models of these rocks suggested by the field, petrographic, and major element contents are further refined using Rb, Ba, Sr, REE (rare-earth element), Th, Sc, and Co contents. There are two groups of relatively undifferentiated plutons asociated with the Butler Hill caldera and Taum Sauk area that could have formed by partial melting of lower crustal rocks. The plutons associated with the Butler Hill caldera (Knoblick and Silvermine granites) could have formed by about 30% aggregate melting of a quartz diorite, graywacke, or subgraywacke. The plutons associated with the Taum Sauk area could have formed by about 30% equilibrium melting of a subarkose or arkose. More silicic rocks of the Butler Hill caldera could have formed by fractional crystallization. The Silvermine granite is internally zoned. Crystallization of plagioclase/biotite/hornblende/magnetite/apatite/zircon/sphene in a ratio of 0.70/0.10/0.15/0.04/0.005/0.003/0.007 from the least differentiated portion of the Silvermine granite could have formed intermediate portions of the Silvermine. Further crystallization of the Silvermine requires more biotite (Ba begins to decrease) and less hornblende, zircon, and sphene (HREE increase) to precipitate and form the most differentiated portions. Also fractional crystallization of undifferentiated Silvermine-type magmas could have produced the sequence of Butler Hill-Breadtray-Graniteville granites as residual liquids, respectively. The early crystallizing mineral assemblage is dominated by plagioclase and biotite, while the late crystallizing mineral assemblage is dominated by quartz, K-feldspar, and lesser plagioclase. The Gneissoid granodiorite in the Hawn Park area has the mineral assemblage and composition of cumulate derived from the Silvermine granite-type differentiation sequence. The associated volcanic rocks could not have formed from melts of exactly the same composition of any of the associated intrusive rocks. Rather, the volcanic rocks formed from melts of slightly different chemistry.