ARTICLE 2: Boulders and Hydro-Mining
Boulders and Hydro-Mining
By Gilbert Hice
Boulders — big or small — can accumulate within a borehole mining cavity in deep placer and result in a catastrophic shutdown of traditional borehole mining processes, but should present no significant challenge for Hydro-Mining to work. Conventional borehole mining operations avoid boulder-strewn placers, which can and do prohibit recovery of rich subsurface placer deposits, as indicated by borehole mining expert G.A. Savanick in multiple articles, including in his ‘Chapter 22.4 Hydraulic Mining: Borehole Slurrying’, SME Mining Engineering Handbook, Oil-Sand Mining section, pp.1934-1935.
Boulders, contrary to some conventional borehole mining wisdom, can be the right size and shape to easily move in a borehole mining cavity current and can actually generate a beneficial trommel effect within the mining cavity by rolling around for better breakage and cleaning of slurry (mixture of gravel, mud and water). Such boulders can also simultaneously undergo erosive and fracturing changes. In Hydro-Mining if a moving boulder settles upon and blocks the Hydro-Mining sump gold trap entrance it may be broken up by jetting impact or drilled through to recover the gold and platinum group metals concentrated in the Hydro-Mining sump trap beneath it. Similarly a pile of boulder debris that has accumulated above the sump trap can be penetrated by a sonic core barrel and a sonic casing string to recover contents of the Hydro-Mining sump gold trap. Boulders or accumulated rock debris should not prevent down-hole sonic jetting equipment from working because certain design features of the proven sonic core drilling system can facilitate both extraction and advancement of downhole equipment in such situations — using acoustic energy, established methods/systems and special apparatus.
The imminent “boulder” question – what happens when boulders are encountered in a Hydro-Mining operation (i.e. in a non-homogeneous boulder-filled, water-flushed cavity within a gold-rich placer deposit being recovered using Hydro-Mining), since boulders come in all sizes and shapes and are proven to stop conventional borehole mining? Facts are – big, room-sized boulders can be drilled completely through in order to Hydro-Mine what’s underneath them (where ground can be very rich and untouched). Further, multiple branches of physics in combination can’t accurately predict all the force interactions, physical phenomena and outcomes involved in a dynamically vortexing and cyclonic Hydro-Mining’s borehole mining cavity, with or without moving boulders. But borehole mining in general has proven to be accurate enough to approximate outcomes of production and issues of challenge at each subsurface mining site, especially with proper pre-mining planning and site assessment. Hydro-Mining’s design is the result of years of gold mining experience and is also significantly evidence-based. Successful deep placer deposit recovery, in spite of boulders, requires applying both well-proven and new innovations in concert that will overcome the challenges that have crippled traditional borehole mining attempts. Boulders will not be a significant problem for Hydro-Mining, especially since they are often associated with the very rich deposits that Hydro-Mining will be targeting, and was designed accordingly to be effective in such conditions. So, good things should happen with Hydro-Mining’s target production in all types of placer, including those with boulders.
There’s plenty of evidence indicating that boulders in a borehole mining cavity can be both disintegrated and pushed (or both simultaneously) by high-pressure jet stream contact and turbulent currents throughout a subsurface jet-mining excavation site. As long as boulders do not disrupt extraction of slurry, which the Hydro-Mining design implicitly addresses (e.g. ceiling slurry extraction, elastic sonic jetting rods, consistent diameters of rods and jetting tools, etc.), boulders can actually benefit the Hydro-Mining process (which is advantageous especially since they are often associated with high-value targets). Further, since boulders do not interfere with sump gold trap content extraction or slurry extraction, they do not require removal from the cavity in order for the Hydro-Mining process to produce high recovery rates/percentages of targeted recoverable resource. Hydro-Mining should be accurate enough following site assessment (especially with core barrel sampling) to borehole mine a valuable deposit positioned beneath a boulder field, therefore avoiding any significant issues with boulders or any other layer of questionable integrity. Appreciating further the advantages of Hydro-Mining with boulders may require a bit of imagination into that which has been empirically demonstrated in the billiard room, on the rifle range, with conventional borehole mining projects and with sonic core drilling rigs recovering core samples — undoubtedly in a few other places as well.
Five additional thoughts to consider regarding boulders encountered during Hydro-Mining:
1) Boulders are generally considered to be any relatively solid rock about 10 inches across (in 3-dimensional diameter) or larger.
2) Boulders can be made up of multiple materials, with different shapes, densities, structural integrity and positional orientation, some having more or less of a tendency than others to be fractured or sheared or pushed when forces are applied (given different material parameters i.e. moduli).
3) A dynamic, chaotic fluid-filled (slurry-filled) sonic borehole mining cavity can be an arena of many interactive forces and factors acting upon and impacting a boulder at any one time, such as buoyancy, friction, gravity, thermal, jetting forces, acoustic wave forces, vortex forces, viscosity, etc.
4) Depending on the multiple factors that act upon a boulder’s physical situation (at any one moment), a boulder may move or may not be moved in a mining cavity, but forces will still be present to one degree or another that can result in changing the boulder’s reality instantaneously, such as by fracturing, eroding or even accelerating or stabilizing the movement of the boulder.
5) Just as a boulder is acted upon by multiple forces in a dynamic mining cavity, the boulder will itself act upon other elements in the borehole cavity (whether the boulder is moving or remaining steadfast), assisting in the subsurface cavity’s trommel effect with cleaning and separating moving slurry components. The slurry components should degrade upon contacting one another and the boulder, everything being in a process of transformation towards more distinct and classifiable slurry material — some as suspended slurry material, such as suspended gold flakes, moving in the fluxing slurry upwards to the surface (extracted through the Hydro-Mining annulus positioned towards the ceiling) while simultaneously other slurry components with higher density, such as big gold nuggets, will gravitate into the sump trap in the floor (for periodic Hydro-Mining core barrel recovery).