Structural Controls On Hydrothermal Flow And Alteration At Sailor's Grave,Coromandel Peninsula,New Zealand

The Sailor's Grave rocky shore platform,located in the east part of Coromandel Peninsula,New Zealand,is a well-exposed hydrothermal altered vein-style Au-Ag-epithermal system.The rock types are mainly basaltic andesite lavas and breccias.The rock is well exposed,highly altered by hydrothermal fluids,and cross cut by faults and fractures.These attributes make it an ideal place to understand the relationships between structural architecture and the associated hydrothermal system,thereby providing insight into possible localization of favorable sites for ore deposition.According to the petrography analysis and XRD analysis,four alteration types have been recognized.That are Phyllic/sericite alteration,Prophylic alteration and Argillic alteration and Potassic alteration.However,there is only one sample might belong to potassic alteration,which located at the linkage zone in the northern part of the study area,which may indicate a relatively shallow paleo-depth(<600m).Hydrothermal alteration intensity in this thesis is interpreted as:Low altered(Low),Medium altered(Mid),Highly altered(High),Highly altered(Very High),and Intensely altered(Max).There are three main vein types in my study area:calcite vein,quartz vein,and quartz+pyrite vein.Geochemical analysis provides a tool to identify the host rock type,identify the geochemical halos and mineralogical halos.Isocon analysis can identify the element mobility.In this thesis,I have come up with a new analysis method mobile/immobile elements ratios(MIM ratio)to understand the alteration halos,alteration intensity and serve as indicator for veining zone and/or possible paleo-upflow zone.The main structures in the study area are NNW-striking normal faults and fractures,which are linked by NE striking normal faults in the north of the study area.However,there also exist WNW striking strike-slip faults and fractures with opposite sense of shear(right and left lateral).This study indicates that one of the highest alteration intensity and paleo-upflow zones is located at the center of Sailor's Grave platform close to the cliff with the highest density of faults and fractures.The other is located at the linkage zone at South Otara Bay platform.The vein density and width also shows a strong correlation with the main faults.For example,the widest quartz veins have a NNE-strike and dip steeply to the WNW and ESE,which has conformity with the main fractures and faults in study area.According to the detailed structural field work,the paleo stresses in the study area are:?₁:135/54(dip direction/dip),?2:332/35,?3:236/8.That may reflect the tilting process with an axis of46°NE and 36°E tilt.