It is common among geologists in the Ghanaian mining environment to hypothesize that whenever hydrothermal gold occurs with pyrite, the pyrite must be fine-grained. This study conducted in the Subika gold deposit in the Sefwi Greenstone Belt, Ahafo used petrographic analysis to characterize (a) the host igneous rocks, (b) identify the role played by these host rocks in the gold mineralization process, and (c) determine the relationship between the gold occurrences and pyrite types observed. Least altered samples (n = 52) were studied under transmitted light, revealing varying amounts of the following dominant minerals: pyroxene, hornblende, biotite, and plagioclase. The mineral modal abundance data was plotted on QAP diagram, and confirmed that the host rocks are gabbro and diorite. Furthermore, the altered samples (n = 70) revealed carbonatization, sulfidation, chloritization and albitization as the alteration types associated with the hydrothermal gold mineralization. Results reveal that the interaction between an ore-forming hydrothermal fluid and the varied mineral modal abundance was likely a major litho-chemical control for gold precipitation. Ore petrographic studies revealed two types of pyrite: coarse pyrite (>500 µm; py 1) and fine pyrite (<500 µm; py 2). The coarse-grained pyrites are porous in the core (py 1a) and massive (py 1b) at the rim and inclusions of gold occurred as cavity- and fracture-fills in them. On the other hand, py 2 are massive and non-porous in nature but contained inclusions of gold only. The nature of gold occurrence in the pyrite-types reflects the timing of gold mineralization in the Subika deposit. Gold precipitation was synchronous with py 2 deposition but might have post-dated py 1a. This study shows that both fine pyrite and coarse pyrite can host gold, which is in contrast to the general idea that coarse pyrite is not associated with gold mineralization in Ghana. Therefore, care must be taken in handling rock samples from drill core, mine/pit exposures or outcrops that contain coarse-grained pyrite. This study reveals that the characterization of the hydrothermal ore system at Ahafo and surrounding deposits must be carefully reviewed to enhance a better understanding of the deposits, which in turn can improve exploration targeting, orebody definition and maximize ore recovery. The findings are applicable to any studies on hydrothermal deposit systems elsewhere in Ghana and the world.