Larvotto Resources Limited (ASX: LRV) has commenced a combined Electrical Resistivity Tomography (ERT) and Induced Polarisation (IP) geophysical survey at its Ohakuri Gold Project, located in the North Island of New Zealand.
“We know we have a lot of gold in the area from old drilling intersections and we know from geophysics undertaken after the bulk of drilling was completed, that this drilling although producing some great results, has not tested the main geophysical anomaly. Luckily for us, we can now use the previous 40 years of work to refine the target zone,” Managing Director, Ron Heeks, said.
“We have been looking forward to starting this geophysical survey to define these zones for some time and after several equipment related issues, we are pleased to advise it has now finally commenced.
“If successful, this survey should provide well defined targets to drill test the conduits that moved the gold to surface from its deep source. We anticipate that the results should be available within the coming weeks.”
The Ohakuri Gold Project is a partially explored epithermal gold system that lies within the Taupo Volcanic Zone. Previous exploration by several companies dating back to the 1970s has delineated a large, lower- grade zone of gold mineralisation.
Significantly, feeder zones that generated this mineralisation were not targeted during these early phases of exploration.
The aim of the current ERT/IP geophysical survey is to both infill and refine the previous broad scale geophysical survey work undertaken at Ohakuri, and to gain more detail at depth regarding the location of the potential Ohakuri and Maleme gold feeder conduits.
These gold conduits have potentially provided mineralisation to the very thick zones of lower grade mineralisation that cover an extensive area within the central portion of the Project.
As highlighted previously, historic drilling into this broad scale mineralisation has produced gold hits including:
• 172m @ 0.41g/t Au • 215m @ 0.21g/t Au
• 160m @ 0.32g/t Au • 170m @ 0.24g/t Au1
Exploration Rationale
Early exploration at Ohakuri commenced over 40 years ago with rock chip sampling of epithermal rocks identified in the incised creeks and river beds that dissect the area. Only the creeks made for worthwhile sampling as of the majority of the Project area is covered by a veneer of very recent, unmineralised, volcanic ash that obscures the rocks below it. The creeks have cut through the ash layer.
The first phases of drilling were focussed on these creek samples. Drilling was largely orientated to test under the creeks that created the anomaly. Numerous exciting intersections of wide but lower grade gold and silver mineralisation were initially encountered and further drilling over a long period by several companies, expanded the area of interest but work was predominantly focussed on following up the original geochemical targets.
Numerous phases of surface geochemistry were also undertaken over the years using several methods. All of which, in hindsight, suffered from the blanketing effects of the overlying ash layer. Over 10,000m of drilling tested the original area of interest without successfully identifying the conduit of gold mineralisation that created the wide zone of gold mineralisation intercepted in drilling. Ergo this can only have come from a deeper source via a mineralising fluid to the surface.
To reset thinking and target deeper and wider areas below the ash layer, the use of geophysics began in 1987. The aim was to identify to the conduit’s mineralisation used to move gold from depth to the surface. As these fluids would have been silica (quartz) rich, they should be resistive to electrical current and locating resistive zones was the aim of the surveys. Several methods of geophysics were trialled over selective areas.
The most meaningful was a broad ESCAN survey undertaken in 2007 by Glass Earth Ltd, which revealed the presence of a deep source intrusion that is probably the source of mineralisation, as the exploration model suggested. Later modelling of the ESCAN geophysics by Larvotto, using more modern processing, also identified several potential gold conduits or feeder zones from the deep source to the surface.
The main potential feeder appears to be oblique to the majority of drilling and as only 2 holes were drilled after the ESCAN survey was conducted, the target was not properly tested. The ESCAN also highlights the majority of the drilling is oblique too and falls outside the broad anomaly and certainly well away from the central core of the geophysical anomaly, especially when the dip feeder zones as indicated by the geophysics is considered.
he prospectivity of the Ohakuri fault area as a gold feeder zone is highlighted by a single hole drilled by Cyprus Gold NZ Ltd (Cyprus) outside of the Central Zone that hit an intersection of zone of gold mineralisation of 10m @ 2.0g/t Au within a wider zone of 35m @ 0.68g/t Au within hole OHCY-19 at the northern end of the ESCAN survey, but outside of the geochemical survey area.
For further information please visit: https://www.larvottoresources.com/
