Condor, is pleased to announce that consultant structural geologist Dr Tony Starling of Telluris Consulting Ltd has completed a study on the structural geology of the La India Gold District.
The study represents a significant step forward in understanding both the structures that host, and the structures that offset, the gold mineralisation in the La India District. At resource scale the work will enhance and improve confidence in future resource models. At regional scale the study improves understanding of the structural framework that controlled the flow and deposition of epithermal gold. The findings will be integrated with the recently collected soil geochemical data to define and prioritise targets for further exploration for hidden deep-seated gold deposits.
Mark Child CEO comments:
"We are delighted with the results of a very detailed report on the structural geology of La India Gold District following a 12 day site visit by consultant structural geologist Dr Tony Starling. La India Project is a low sulphidation epithermal gold system, which is structurally controlled and complex e.g. the multiple phases of faulting in the historic past channelled the upflow and precipitation of the gold bearing fluids. The study represents a significant step forward in understanding the structure that hosts the gold mineralisation at La India Project. The report details 33 exploration targets derived from the structural setting, 23 of which have known gold veining at surface. The targets require follow up work on the ground and prioritisation before an exploration programme can be planned.
The structural geology report draws on the most recent academic and field studies to establish the position of La India Project within the Tertiary magmatic arc and tectonic framework. The report focusses on the better documented core resource area of La India, America and La Mestiza vein sets, and as far out as the Dos Hermanos Vein to the southeast and the Cristalito, Real de La Cruz and Cacao prospects to the north and east. This area encompasses the entire independent mineral resource estimate for la India Project which currently stands at 18.1M tonnes at 4.0g/t gold containing 2.32M oz gold.
The La India District has been subject to three principal deformation phases during deposition of the host Coyol Group volcanic rocks in the early to mid-Miocene:
D1 occurred during the mid-Miocene as NNE-SSW directed extension caused by subduction zone roll-back and then rebound from slab detachment. This event imparted the dominant WNW structural grain and development of NNE transfer faults such as the Highway Fault. The emplacement of a series of rhyolite flow domes such as at Real de La Cruz and Santa Barbara appear to be associated with the transfer faults. This event is considered pre-gold mineralisation, although gold mineralisation at the end of the event on WNW and E-W veins is not discounted.
D2, the main gold mineralising event, is likely to have occurred sometime during the mid- to late- Miocene during the slab detachment phase and a pause in volcanism. Regional extension rotated clockwise to an ENE to E-W direction likely due to the relative easterly motion of the Caribbean Plate. During this phase, the WNW structures were reactivated as dextral transtensional faults resulting in dilation and concentration of gold mineralisation along NNW striking jogs and newly created NNW-trending extensional faults. The development of steeply dipping to near vertical high-grade shoots on the La India Vein is attributed to the interaction between pre-existing dextral transtensional WNW faults and the more dilational NNW-striking La India fault. Pre-existing structures such as the Highway Fault were reactivated again as transform or transtensional faults. Another pre-existing deep seated NNW structural fabric visible in geophysics and to a lesser extent topography appears to be associated with the principal La India, America and La Mestiza vein sets and may have formed a deep-seated hydrothermal fluid pathway.
D3, which started in the early Pliocene and continues to this day, was initiated by a return to a subduction zone regime and the subsequent collision of the Cocos Ridge with the Caribbean Plate at Costa Rica resulting in dextral strike-slip motion along the forearc zone in Nicaragua. At La India this event is seen as a return to N-S to NNE-SSW directed extension that implies a partitioning of oblique subduction into pure strike-slip and extensional components. Reactivation of some fault veins occurred during this phase with graben development in the centre of the America Vein Set and the deep-seated El Tanque Graben, suggesting significant extensional movement. This phase is also associated with reactivation of the NNE Highway Fault and another parallel fault running up to Real de La Cruz, this time as transtensional faults with downthrow movement to the east of a large block incorporating La India South – Mojarra, Central Breccia – Cacao and the Real de La Cruz and Santa Barbara areas. Gold mineralisation channelled by these faults at Central Breccia, Cacao and possibly at Real de la Cruz are interpreted as the upper levels of epithermal mineralisation, perhaps reflecting hydrothermal upflow zones. Some important prospect-scale structural interpretations associated with D3 structures include:
Listric faulting and rotation of hangingwall blocks as imbricate listric fault blocks on the La India structure as evidenced by inclined bedding.
The Highway Fault terminates against the La India Fault along the hangingwall of the vein with extension being absorbed by downthrow of La India South. This provides an elegant explanation for the deeper-seated mineralisation at La India South and the position of the andesite host.
The high-grade gold mineralised breccia at Real de La Cruz is gold mineralisation on a NNE fault parallel to the Highway Fault whilst the E-W to WNW trending stockwork veinlets reflect the regional structural grain.
Future gold exploration, particularly for hidden deep-seated gold mineralisation should target the NNW striking jogs on WNW faults, NNW-trending linking faults that formed dilational zones in the D2 deformation phase, and also the intersection of NNE faults such as the Highway Fault with cross-cutting NNW- and WNW-trending faults. Downthrow of the rock masses to the east of the Highway Fault, the centre of the America Vein Set and the deep-seated El Tanque Graben suggests that these areas are likely to have suffered the least erosion and are therefore the most likely to have preserved the entire boiling zone beneath surface.
Vein textures of surface exposures of the known gold prospects within these downthrown blocks such as Central Breccia, Cacao and Real de La Cruz confirm the high-level of gold mineralisation and soil geochemistry at El Tanque supports this block as exploration targets for hidden deep seated gold mineralisation. Thirty-three targets that meet these structural criteria have been identified in the study, twentythree of which have known quartz veining at surface. All the targets are being assessed by detailed geological field mapping with the structural targets that occur in the downthrown blocks and with anomalies identified in the regional soil geochemical data prioritised for follow-up exploration.