Runruno project resides within the Caraballo district, whose geology largely consists of pre Cretaceous to Early Cretaceous basement rocks consisting of ophiolite and schist underlying Late Cretaceous to mid-Miocene age volcanics, volcanoclastics and sedimentary rocks. The strata are intruded by the Upper Miocene Palali – Cordon Complex which is overlaid by Pleistocene lava flows, pyroclastics, marine sediment and Pliocene Matuno Formation.

Structurally speaking, the region is largely cut north south and moderate to shallowly dipping extensional structures. The area also has NW-trending, steep crosscutting arc-parallel faults which are interpreted as strike slip features. The area has undergone intrusion and uplift subsequent to and during the formation of the Palali-Cordon Alkali Intrusive Complex and is interpreted as an intra-arc basin.

Runruno sits at the intersection of the borders of two district-scale calderas, major NW and NE fault lines and a number of small volume, late composite volcanic centres. Mineralization at Runruno is hosted by a shallow-dipping fault zone of potassically-altered sericitized and brecciated tuffs and andesites which have been variably pyritized and silicified. Gold mineralization is preferentially hosted within fractures, faults, and breccias.

The style of gold mineralisation in Runruno is mostly as fine disseminations associated with pyrite and/or molybdenite. The original of the mineralisation is believed to be fault controlled. Gold mineralisation is hosted by low angle structures enveloped by bluish to gray colour altered wall rock containing fine-grained sulphides, molybdenite and tennantite. Gold occurs both as megascopic native particles and as microscopic inclusions in pyrite. The small nature of these intrusions results in the gold mineralisation at Runruno being refractory.

Runruno is a conventional drill and blast open pit mining operation. The space available for waste dumps in the mine is constrained by the short strike length of the orebody and steep terrain. Consequently, the waste material from the pit is currently placed in ex-pit dumps, with the pit being developed to accommodate in-pit dumping to progressively fill the mining void. The open pit area is 600 metres x 1,500 metres, with mining taking place in stages longitudinally along the ore body to provide an average strip ratio and consistent ore delivery to the plant.

Mining improvements
A number of improvements were made with respect to operating the Runruno open pit, which ensured the pit can operate smoothly until the end of mine life. The Runruno pit runs through Malilibeg Fault, however prior to 2019, there were no considerations for the fault in the mine design, which resulted in a number of unexpected pit failures starting in 2018, which effected the mining rates at Runruno. The new management redesigned the pit to put in a cutback, to satisfy the required factor of safety for the pit walls.

In addition, the original mine design had major issues with the design of the mine access. As previously mentioned all the mined waste gets placed back in the Runruno pit and thus pit design is staged, where material from a following stage is place back into the pit viod created from the previous stages. Previous design didn’t properly plan access ramps from one stage to another and without the redesign and proper sequencing the mine would have ended up being waste bound in 2021 and thus the production would get shut down. This has now been corrected with the redesign of the mine wide ramp system and the mine will become very efficient by Q4 2021 with the waste mined to be backfilled in the stage 1 pit void, thus decreasing the amount of trucks required in the pit, lowering the overall cost base.

Finally, there was a distinct lack of definition drilling and thus the understanding of the mine reserves going forward. This is being corrected with significant money spent on reserve drilling in 2020, with more to be expected in 2021. This will increase the confidence in the mine reserves in the stages 2 & 3, with further work required in stages 4 & 5, thus allowing for better forecasting and short and medium term mine planning.

The small grained, typically less than 10 micron, nature of the Runruno gold mineralization in the pyrite makes Runruno ore unsuitable for conventional CIL processing. The Runruno processing plant is designed to treat these difficult to recover gold ores using state of the art technologies.

The ROM ore from Runruno is crushed prior to milling in a single-stage SAG mill. Gravity recoverable gold from the mill discharge is recovered in a gravity circuit achieving approximately 25% gold recoveries. This is followed by the well-established bacterial leaching (BIOX®) technology, which utilises cultivated bacterial which converts the sulphide minerals and exposes the gold for subsequent cyanidation. The target sulphur grade required from flotation for the BIOX® process to run optimally is 17%.

After leaching in CIL, Runruno utilises the ASTER™ (Activated Sludge Tailings Effluent Remediation process), which is a biological cyanide destruction process that allows for a mo ........