For a Blina Alluvial Prospect overview watch our field video.
Figure 1: Blina Alluvial Prospect Location
GIB Blina Diamond Project – Key Points
GIB Bulk sampling and trial mining campaign
8.43 carat Fancy Yellow diamond previously recovered from the Blina Project alluvials (GIB ground) during Terrace 5 sampling (Pit 82).
1.0 Blina Diamond Prospect, Ellendale WA GIB 100%
Gibb River Diamonds Limited (‘GIB’ or the ‘Company’) operates the Blina Alluvial Prospect in the Ellendale Diamond Province of WA's Kimberley Region. The project consists of three granted mining leases and various exploration leases (Figure 1) situated 110km east of Derby and adjacent to the currently-closed GIB controlled Ellendale 9 diamond mine.
A diamond bearing alluvial palaeochannel named Terrace 5 extends over some 40km of the GIB project area, with channel widths of 200m to 500m. The largest diamond recovered to date from Terrace 5 weighed 8.43 carats, with stones larger than two carats common. A significant number of the diamonds are Fancy Yellows.
The key to exploring the Terrace 5 diamondiferous channel is to find the best alluvial trap sites which are most likely to host the highest diamond grades, these trap sites usually occur around the sediment/bedrock contact.
GIB Minerals has completed a ground geophysics survey using the latest in Ground Penetrating Radar (GPR) technology and the Company believes we now have a fast and inexpensive breakthrough technique which can discover these trap sites and their highly prospective diamondiferous gravels. Company trenching programs have also discovered extensive areas of unsampled, shallow and highly prospective alluvial gravels3 which also require testing.
GIB has merged historic drilling, trenching, bulk sampling, trial mining, indicator mineral sampling and geophysical data with the latest state of the art GPR data to generate high grade alluvial diamond trap site targets on the proven diamondiferous channels.
GIB is pursuing a GPR-driven systematic bulk sampling program of these prospective gravel targets which will define the extent and grade of the diamondiferous gravels. The best grades will be trial mined; see field video.
2.0 Blina Prospect Diamond Valuation
An independent appraisal (Nov 2017) on the data from a 1,497.57 carat parcel of diamonds previously mined from Terrace 5 was conducted. This gave a price of US$389 per carat (A$505 per carat). This is a 63% increase on the previous valuation of US$238 per carat made in April 2006.
This substantial price increase is mainly due to the greatly increased pricing of the fancy yellow component of the parcel which has gone up by 131% to US$3,391 per carat (A$4,403 per carat). The previous valuation of the Fancy Yellows in 2006 was US$1,466 per carat. The Fancy Yellow component now constitutes 62% of the value of the whole parcel (up from 50% in 2006).
The largest stone in the valuation parcel was a Fancy Yellow stone weighing 8.43cts. This diamond has an estimated value of US$44,482 which is the equivalent of US$5,277 per carat; see ASX Release.
The Company could expect to recover very similar diamonds from the GIB Blina alluvials.
2.1 Valuation Composition by Quality
The valuation parcel had a Gem content of 38%, Near-gem of 55% and Industrial of 7%. The combined Gem and Near-gem content of 93% could be considered high by world standards.
3.0 Terrace 5 JORC (2012) Exploration Target
The JORC (2012) Exploration Target for the Terrace 5 alluvials is from 700,000 to 1,000,000 cubic metres at a grade of 2.3 to 4.1 carats per cubic metre, for contained diamonds of 1.6 to 4.1 million carats.
Table 1. Exploration Target Summary
(carats per cubic metre)
Figure 2: Section View of Eroded Lamproite from E9
This Exploration Target is based on estimating the amount of ‘Missing Diamonds’ which have been eroded from the E9 pipe (Figure 2) and have ended up in the Terrace 5 palaeochannel (Figure 1). A full technical summary is detailed in the recent GIB ASX Release.
This maiden JORC Exploration Target demonstrates the potential of Terrace 5 to deliver very high grades on what would be a relatively simple, shallow, low capital cost and low operating cost alluvial mining process.
Previous explorers lacked a method of indirectly mapping the prospective bedrock-cover contact. The highly successful recent GIB geophysical survey using Ground Penetrating Radar may well prove to be a gamechanger for this project by quickly and inexpensively defining the highest quality diamond targets at this contact. The potential for discovering bonanza grades within these newly defined trap site targets presents an exciting and significant upside.
Figure 3: Section: Ground Penetrating Radar Targets
Note the previous explorers pit BS6 which missed the prospective interpreted pothole which shows up on the GPR data.
4.1 High Grade Alluvial Diamond Trap Sites: Examples
The bonanza grades and returns that can be found within high grade alluvial diamond trap sites make these systems a highly desirable target for alluvial diamond miners. An example of the type of high grade pothole trap sites GIB is looking for at Blina is shown in the photo below taken at the Auchas Diamond Mine on the Orange River in Namibia.
Figure 4: Auchas Diamond Mine, Namibia. Potholes
4.0 High Grade Diamond Targets Identified
By combining GPR and historic pitting and trenching data, GIB has identified two discrete channels within Terrace 5. These have been named Channel 1 and Channel 2 (Figure 2). Previous testing on Channel 1 indicates it is strongly diamondiferous, Channel 2 is untested.
Channels 1 and 2 are deeper, and presumably older, than the other defined Terrace 5 gravels in the area. The historic bulk sampling which took place over the newly defined Channel 1 gave some of the best results within the Terrace 5 system, with grades up 10.5 carats per hundred cubic metres (cphm3), see Table 2.
Table 2: Bulk Sample Results from Channel 1
Diamond grade (carats per hundred m3)
Average diamond size (carats)
Largest Stone (carats)
Within Channels 1 and 2, GIB has identified 139 GPR targets, which the Company believes are the most prospective areas within the entire Terrace 5 system. These 139 targets have minimal overburden (2 to 8 metres), lie within proven diamondiferous channels and show up on the GPR as excellent potential alluvial trap sites.
Figure 5: GPR High Grade Targets
5.0 Trenching of Gravel Targets
The company has conducted various trenching programs over the Blina Prospect and has discovered numerous shallow, untested gravel target areas which conform our geological interpretations of Channels 1 & 2 containing highly prospective gravel, including areas of trap sites.
Gravel Target Areas - Untested Gravels in Trenches 1 and 4:
Trench 4 rounded gravel clasts, many of which are partly saprolitised (turned to clay by weathering)
6.0 Achievements at Blina So Far
7.0 Blina Prospect Operational Goals 2020
GIB is pursuing a GPR-driven systematic bulk sampling program of these prospective gravel targets which will define the extent and grade of the diamondiferous gravels. The best grades will be trial mined