The Dublin Gulch intrusion-hosted gold deposit, Tombstone plutonic suite, Yukon Territory, Canada

Abstract.

The Dublin Gulch intrusion is a member of the Tombstone plutonic suite, a linear belt of middle Cretaceous intrusions that extend across the Yukon Territory. Like many of the intrusions in this suite, the Dublin Gulch intrusion is associated with several different zones of gold and tungsten mineralization, within and immediately adjacent to the intrusion. The Eagle zone (50.3 Mt @ 0.93 g/t gold), located in the southwestern part of the Dublin Gulch intrusion, hosts the most significant concentration of gold in the area. The gold occurs in a broadly east–west-striking, steeply south-dipping series of sheeted veins. The veins consist of early quartz–scheelite±pyrrhotite±pyrite±arsenopyrite, and are associated with K-feldspar±albite alteration envelopes. These grade out to and are overprinted by sericite–carbonate±chlorite alteration. The same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold. The gold occurs with molybdenite, lead–bismuth±antimony sulfosalts, galena, and bismuthinite. Gold correlates strongly with bismuth (r ²=0.9), a relationship common to several intrusion-related gold deposits, but has a poor correlation with all other elements. Tungsten and molybdenum have a weak inter-element correlation (r ²=0.55) and paragenetically pre-date the majority of gold precipitation. Lead, zinc, copper, silver, antimony, and arsenic have moderate to strong inter-element correlations (0.58 to 0.93). The change from tungsten-bearing mineralization through to gold–bismuth-rich ores with elevated syn- to post-ore lead, zinc, copper, silver, antimony, and arsenic can be grossly correlated with a change in hydrothermal fluid composition. Early scheelite-bearing quartz contains primary CO₂-rich fluid inclusions, which are post-dated by secondary inclusions with higher salinities (up to 15 wt% NaCl equiv.) and less CO₂. These latter inclusions are interpreted to coincide with the later gold–bismuth and base metal mineralization. The favored genetic model is one in which early CO₂-rich fluids exsolved from a magma with an initially high CO₂ content, but progressively became more saline and H₂O-rich as the system evolved.