On 24th January 2013 Rumble announced it had discovered a unknown major artisanal mining site on its Bompela permit, with an estimated 4000 plus artisanal miners. The area is approximately 400m long by 200m wide. Bompela is the furthest North West permit of the Derosa Project and covers a landholding of approximately 250km². The artisinal site is located on a structure which is over 30km long with no previous exploration and will be a focus of further target generation.
The artisanal mining was triggered by the discovery of gold mineralisation on the side of a small laterite capped hill.
Following the discovery, Rumble engaged SEMS Exploration (“SEMS”) a leading mineral exploration and mining consultancy company in West Africa, to undertake a range of programs, including:
- Field mapping and prospecting;
- Detailed geological mapping and sampling;
- A regional reconnaissance over the permit area.
Figure 1: Map showing location of the Bompela Gold Discovery Figure 2: Map showing Bompela on a 30km structure
Bompela Open Pit and New Artisinal Site
On the commencement of the programs Sems discovered the Bompela artisanal area has significantly increase its potential with the artisinals gold miners excavating an open pit. The open pit is a rare sight in West Africa as the artisinals generally follow the quartz structures and only remove the minimal amount of dirt to maximise their returns. To put this into context the rocks and soils are being removed by primitive techniques in hammers, chisels, buckets and ropes. The open pit and sampling completed by Rumble, suggests that the gold is not only in the quartz veins but also in the granite host rock which is important when looking for a deposit that could host bulk tonnage as well as suitable grade.
SEMS also uncovered a new active artisanal site located 850m along strike from the main Bompela artisanal site. The area between the 2 sites is covered by alluvial material and is a high priority target for the Company. Mining is very active at the new site, which is mostly focused on the hill slope beneath the laterite escarpment. Apart from the two main sites, artisanal miners are also digging test pits along the laterite escarpment north of the main site.
Photo 1: Artisanal miners excavating sections of the Bompela Open Pit Photo 2: Image showing the proximity of both Bompela Artisanal Sites
Detailed Litho-structural and Regolith Mapping
The mapping and rock sampling of the Bompela workings indicated the presence of structurally-controlled in situ vein-type gold mineralisation located within a strongly altered granodioritic pluton. The mapping also indicated that the host rock unit is commonly red pyrite-altered granite. Some specimens of red granite also contain up to 3% pyrite with minor chalcopyrite. Shears filled with quartz veins and chlorite was observed in the artisanal open pit. These veins and the granitoid stock are being targeted by the artisanal miners.
The results of the field mapping showed that the area is widely covered by alluvium and laterite ridges and plateaus. Alluvium covers large parts of the area of interest which hide the structures undercover with the artisanal miners only able to target the outcropping laterite hills leaving prospective gold bearing structures undiscovered.
Rock Chip Sampling of Outcrops
In the first program SEMS collected 350 grab samples with significant results including 28 samples >1g/t Au and 34 samples ranging from 0.5 to 1.0 g/t Au with the highest being 16.2g/t. Over half of the samples returned a value of >0.1 g/t gold or 100ppb, which is an excellent result from this sampling program which was focussed on waste rock from the artisanal mining.
In the second program Sems collected a further 42 grab samples of pit dump material that included quartz veins, fresh white granite, fresh red granite, amphibolite and weathered granite. The samples were from the main artisanal mining area at Bompela and the new active artisanal site located 850m southwest of the main workings. The grab samples returned significant results including 8 samples >1g/t Au with peak values including 24.5 g/t, 7.2 g/t & 6.46 g/t Au. It is interesting to note that although the peak gold values are from quartz veins the samples taken of the host granite are also highly anomalous averaging 0.9 g/t Au where no quartz veining is present.
Figure 3: Map showing the main artisanal site, new site, Photo 3: Artisanals using hammer and chisels, buckets and ropes extent of workings and soil gold anomalism
Ground Geophysics Survey
The result of field mapping shows that the area is widely covered by alluvium and laterite ridges and plateaus. Alluvium covers large parts of the area of interest which hide the structures undercover. The artisanal miners are only targeting the outcropping laterite hills. A program of ground magnetics was completed to compliment this data set by providing detailed magnetic data in order to determine geological continuity under these areas of alluvial cover.
SEMS completed a high resolution ground magnetic orientation survey over the Bompela prospect. The survey area in the vicinity of Sissilé, Burkina Faso, measured 3km x 2.5km, and an accumulated 170 line km were surveyed.
Ground magnetic survey surrounding the Bompela artisanal site indicates continuity of the geology between the main artisanal sites. Essentially this means that the rock unit which is hosting gold at the Bompela artisanal site is likely to be continuous under the alluvial cover, making the areas in between and underneath the two artisanal sites highly prospective.
The gold mineralisation at the Bompela workings is contained in quartz veins and the alteration zones adjacent to the veins. Most of the quartz veins are hosted by granitoid with hydrothermal alteration around the veins appearing to have altered the white granite to a red, or dark pink, granite. Sulphidation with the addition of pyrite and chalcopyrite is also present.
This style of mineralisation is similar to that of many other granitoid-hosted gold deposits of the Eburnian age in West Africa (Ghana especially). Examples include Perseus Mining Ltd.’s Edikan mine (ASX: PRU) and Xtra-Gold Resources deposit at Kibi (TSX: XTG). These types of deposits typically consist of sets of moderately dipping quartz veins up to 1 m in thickness with wall rock alteration around the veins. Gold is found in the quartz veins and the alteration zones. These granitoid-hosted deposits usually occur near the margins of the granitoid where competency contrasts occur between the granitoid and the country rock.
Treatment of ore
Most of the ore produced by mining is processed at the miners camp where it is crushed, either by hand or machine, put through a sluice box, and what is gathered in the carpet is subsequently panned.
One group have been buying crushed material and taking it to this processing plant. The plant consists of many holes dug into the ground and lined with plastic sheeting. The crushed material is placed into two holes either side of a deeper pit. Cyanide solution is then put over the crushed material to leach the gold. The gold-bearing solution then passes through small pipes into the deeper pit where it is collected.
Photo 4: Solution ponds being used to extract gold Photo 5: Sluicing operations to recover gold
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