Tectonic Evolution of the Southern Negros Geothermal Field and Implications for the Development of Fractured Geothermal Systems

Table 1

Summary of field characteristics of the two fracture groups mapped in SNGF.

	Group 1	Group 2
Fault rocks	Cohesive and cemented (cataclastic)	Generally noncohesive/poorly cemented Open fractures in some
Key alteration minerals	Abundant pyrite; Amorphous silica; Quartz; Rare Cu sulfides	Abundant clays; Quartz; Native sulphur; Zeolites, calcites, and gypsum
Kinematics	Mostly E-W (+/−) sinistral	Mostly NW-SE oblique dextral
Host rocks	Older Southern Negros Fm.; Host has been completely altered previously	All lithologies; Both altered and fresh rocks
Alteration pattern	Restricted to fractures	Diffuse or restricted to fractures
Other key observations		Usually related to recent (active/inactive) thermal activity