Epithermal gold deposits can be broken down into three main subtypes: High-sulfidation systems Intermediate-sulfidation systems Low-sulfidation systems Typically, low-sulfidation deposits are higher-grade and lower-tonnage, while high-sulfidation deposits are lower-grade and higher-tonnage. As the name suggests, intermediate-sulfidation deposits fall in between. Gold is not always the dominant metal in epithermal deposits. Metals ratios vary widely among deposits and even within a given deposit. Sometimes these deposits hold more silver than gold; this is the case for the Fresnillo mine, which exists in a district characterized by low-sulfidation epithermal quartz-carbonate veins. Silver-to-gold ratios are generally higher in low-sulfidation deposits than in high-sulfidation deposits, which tend to have more gold than silver. All three deposit subtypes form under similar circumstances; however, intermediate- and high-sulfidation deposits can form at greater depths with vein systems trending at further depth. Unsurprisingly, high-sulfide deposits tend to be richer in sulfides, and they may contain pyrite and enargite in addition to gold and silver. These higher-sulfide epithermal deposits tend to be linked to porphyry deposits. The Toodoggone district of Northern BC, Canada, is a classic example of epithermal gold-silver and copper-gold porphyry systems occurring together in the same geological setting.