Page 249 - Caldera Volcanism Analysis, Modelling and Response

224 W.U. Mueller et al.

A

B

Figure 16 Hydrothermal carbonate alteration model of a submarine caldera is primarily based
on the Hunter Mine caldera with attributes of the Normetal and Sturgeon Lake calderas. (A)
General alteration patterns with an early phase of near surface silici¢cation and an extensive
semi-conformable alteration zone which discordant at discharge zones. (B) Carbonate altera-
tion pairings indicate lateral change across strike of the caldera from focused to more distal
reaches. Silici¢cation at depth is shown in this diagram but is contemporaneous with the
near-surface silici¢cation shown in A. Note the importance of the subenvironments and the
polymetallic deposits in the volcaniclastic deposits, wherein the largest VMS deposits are
favoured at the caldera wall.