ARTICLE 4: Gold Panning and Hydro-Mining
Gold Panning and Hydro-Mining
By Gilbert Hice
Anyone who has ever had a chance to pan for gold understands that the process is relatively straight-forward, often requiring significant low-back activity and elbow grease. The process of gold panning, American ‘49er-style, is based around the idea that gold is heavy so it usually sinks through gravel to the bottom of the pan during the action of cleaning and agitating the contents of the flat-bottomed ‘49er-type gold pan. However, an experienced gold panner also knows that gold pieces are soft and can take many shapes and sizes, some forming small flat flakes that tend get suspended in the water and even float out of the pan easily with “light” gravel and sand as water in the pan is swished back and forth across the pan’s contents. Gold that is in a gold pan one moment can be lost the next even with great care and attention to the basic process. This is one reason so many gizmos, solutions and gadgets are sold promising to recover gold – a better mousetrap is always out there. But catching gold isn’t like catching snowflakes that just melt away in your hand; recovery is both science and art, with the fundamentals of using a basic 49er-style gold pan being time-tested and true for getting positive results, on any scale.
Using the American ‘49er-style, the panning process, of course, begins by placing a scoop of sand, mud and gravel mixture (i.e. slurry), hopefully containing some gold, into a flat-bottomed gold pan with sloped sides. Water is then introduced into the pan with the process using water from a tub or creek to proceed with panning the contents. The gold panner shakes and vibrates the pan, moving it with a circular, back and forth action forcing the mixture of water, gravel and sand into somewhat of a mixed homogeneous slurry that uses a flow of cleaner water from the creek or tub. Cleaning all of the material in the pan is important to the process’ success. Every piece of material in the pan should be washed clean as possible with hand-action, water movement and rock-to-rock contact creating a solution that allows the gold and heavier particles to gravitate towards the bottom of the pan leaving lighter material above. After washing the materials in the pan, the next step is to begin removing as much of the cleaned lighter non-gold material from the pan while continuously agitating the slurry to concentrate the gold on the pan bottom. This is done by a circular and vibratory motion of the pan and also by using one’s hand and creek water movement to skim off the upper and lighter material out of the pan. Large cleaned stones are also examined and removed when possible. This process is repeated over and over again until there is very little “light” material remaining in the pan and the heavier material becomes concentrated in the bottom of the pan. At some point during the process it becomes apparent that a pocket/collection of heavy material reveals itself in the bottom of the pan. The pocket is usually black, which is a composition of black sand consisting of many different heavier elements, (like magnetite, cassiterite, garnet, platinum), and of course the very heavy gold nuggets looking like stars in a night sky. Nuggets and large flakes of gold are often selected out of the black sand with an eye-dropper or tweezers and placed into a separate container. Often many small particles of gold, called collectively gold flour will aggregated in the black sand but are too small to see with the naked eye. Such particles, mixed into the black sand portion, require a magnifying glass or microscope to see and can be isolated using other specialized separation processes from other non-gold particles, once a significant amount of black sand has been collected making additional effort and result beneficial.
So, in comparison to 49er-style panning, but deployed to recover gold on a commercial scale is the Hydro-Mining process recovering large-scale deep deposits of gold — a concept of using an underground “giant gold pan” (GGP) that can be 30 feet wide and ten feet deep, or bigger. It can be created underground as part of a borehole (i.e. drill hole) mining process using high-pressure water jets, used to disintegrate, wash and separate a sub-surface gold deposit, which is discovered by core sampling using a sonic core drilling rig. The new patented Hydro-Mining process uses the concept where “light” slurry materials are removed from the GGP through a rod-adjacent space connected to a surface processor simultaneously with “heavy” precious metal-laden materials being collected in a pocket (i.e. sump gold trap) at the bottom of the GGP. The sump gold trap is removed periodically to the surface using a sonic core barrel, much like using an eye dropper in gold panning. Valuable material should not escape the Hydro-Mining process, which is fundamentally designed to create an underground giant-sized gold pan with a corresponding hydraulic circuit to potentially recover a deep placer deposit of gold using a hi-tech process that has various steps in common with using a hand-held American 49er-style gold pan. This is in contrast to the conical-shaped batea-type of gold pan, which is another shape of gold pan also having common functionality related to Hydro-Mining, incorporating vortex action to help separate slurry layers, discussed below in more detail.
Regarding the Hydro-Mining process, once core sampling through a drill hole identifies a gold deposit deep beneath the ground surface, a special jetting tool is attached to the sonic core drill rig and inserted on a rod string into the ground through the borehole to the level of the gold deposit discovery. This can be done immediately upon discovering the deposit. Such a deposit can be hundreds of feet deep. Lots of high-energy water is then pumped along with vibrating energy into the underground deposit site using high-intensity water jets that essentially begin forming a underground water-filled cavity, like a giant-sized gold pan, consisting of a space that can be 30 feet across or more and many feet deep. This subsurface cavity, also considered to be shaped like a biscuit or cone, has a central hole/depression in its floor called a sump gold trap. High-pressure pulsing jets that chew up the deposit rotate and move up and down forming dynamic turbulent slurry generating layers of “heavy” and “light” materials in the GGP. Stones, sand and gravel are cleaned and broken in the GGP using hydraulic and vortex forces while simultaneously recycling water with “lighter” material moving up to the surface using hydraulic forces though a space between drill rod and casing called an annular space. Unlike a small hand-held gold pan the underground GGP does not move, but the jet streams that are attached to the drill rig do move, as they cut through the deposit and water-filled cavity, causing the water to move and circulate violently in the GGP, forming multiple layers of moving slurry helping to agitate “light” slurry material up, into and through the annular space called an annulus, and out of the GGP onto the surface, where it is collected and processed The heavier material with non-suspended gold nuggets settles to the bottom of the GGP, collecting and concentrating in the sump gold trap.
Gold recovery efficiency, whether with the GGP or with a hand-held gold pan, is a function of effective cleaning of the gravel and sand, with “light” slurry material being moved up and out of the pan as quickly as possible. With the Hydro-Mining process the “light” slurry, which may contain suspended gold and platinum, is lifted out of the GGP to the surface where it is collected in a processing plant as water is separated for recycling to the jet pump. “Floating/suspended” precious metals are separated from the slurry by the processing plant as water is filtered and reused by the surface process, which recirculates water back into the GGP through the jets. The Hydro-Mining process periodically recovers the concentrate of “heavy” slurry that collects in the sump gold trap using a sonic core barrel. Boulders are left in the underground GGP, pushed around, broken and washed by dynamic jet streams and vortex forces, while the heavier materials, such as gold and platinum, gravitate into the trap. No blockage should occur of “light” slurry intakes to the surface processor, which is implicit to the new dynamic design, since the fluctuating intakes are off the floor and positioned near the ceiling of the GGP. Blockage of underground pump or eductor slurry intakes can be a big problem with conventional types of borehole mining designs that are positioned near the floor of the mining cavity. But a main advantage of using Hydro-Mining’s system of cleaning the underground GGP slurry material is in its efficient “light” slurry recovery by continuously agitating the “light” slurry off the top of the underground swirling slurry pile. This increases the rate in which the “heavy” slurry can settle to the floor of the GGP and into the gold sump trap just like in a ‘49er-style gold pan. This process is facilitated by combining the energy packages of hydraulic jet pump and sonic head, along with the patented idea of incorporating an eductor coupling manifold system, which uses many small eductors, to help lift “light” slurry from the GGP simultaneously with jetting while settling the heavier slurry to the bottom of the GGP.
The Hydro-mining eductor coupling manifold system should facilitate flow of lighter suspended material out of the GGP by minimizing lift resistance, i.e. decreasing drag coefficients, and by enhancing effective hydraulic lift in the hydraulic circuit. The slurry eductor recovery system can move “light” slurry up through the annulus for extended distances to be recovered at the surface. This is of course similar to the action of removing lighter material from the top layer of the gold pan material, leaving the heavier material to continually settle to the pan’s bottom.
The Hydro-Mining system is designed to dis-aggregate and wash a gold deposit while creating a GGP — removing “light” material from the GGP while simultaneously concentrating “heavy” material in a sump gold trap at the bottom of the GGP. A surface processor separates water from particulates, which can then be further separated and classified depending on their specific qualities. During the process a sonic core barrel periodically collects the sump trap concentrate, which is similar to using an eye-dropper when recovering gold nuggets from black sand in a hand-held gold pan. Large gold nuggets six to seven inches in diameter can be recovered intact using an 8 inch sonic core barrel. Big gold nuggets are rarer than big diamonds. The GGP can be created hundreds of feet deep, with a gold trap being cleaned and made deeper as the GGP is made deeper with bigger deposits. Twenty cubic yards an hour should be easily recovered from the creation of a GGP even hundreds of feet below the surface, based on other but less advanced borehole mining designs. Once a subsurface mining deposit is cleaned of gold, the cleaned and washed “light” slurry gravel can be returned to the underground GGP mining cavity, pumped back with very little environmental disturbance compared to other types of mining methods, such as shafting or open-pit mining. When gold panning, the panning site should never be left looking like the land has been assaulted. The same is true for Hydro-Mining, an earth-friendly design.
In its most fundamental essence Hydro-Mining is designed to function, in part, a lot like a scaled-up version of the tried-n-true traditional 49er-style hand-held, flat-bottomed, gold pan, but with the added benefit of integrating technological advances for commercial-scale recovery with 21st Century style — Hydro-Mining…but there is more.
The ‘batea’ gold pan design and Hydro-Mining
A batea (known also in early 1900s as a Mexican gold pan), is a type of gold panning apparatus shaped like a cone with its point (apex) down, made of many materials including wood and steel. It is a ‘for panning’ design found, to one degree or another around the world, used commonly for panning gold and precious stones. It functions somewhat differently than an American flat-bottomed gold pan to separate gold from slurry. American ‘49er gold pans work primarily by a back-and-forth agitating motion, settling the heavier material out of a slurry mix by gravitational and inertial forces, primarily. The operation of a batea, on the other hand, is different and probably more similar to what Hydro-Mining is designed to do with a conical shaped mining cavity having a sump gold trap at its apex, though Hydro-Mining will certainly function using features of both types of gold pan design. It has been noted by many references that the batea design is more efficient than the American flat-bottom gold pan and that American pans are becoming more like bateas to gain more efficiency. The batea apparently works like a primitive hydrocyclone mechanism creating a central vortex as a result of manually turning/spinning the pan, which conical shape decreases velocity (and increases pressure consistent with the Bernoulli Principle) peaking its pressure at its bottom apex — thereby generating a centralized vortex effect that flushes less-dense material upward, which overflows the lip being forced out of the batea.
In other words, heavies are forced into the bottom apex of the batea, while lighter stuff gets vortexed up and out through the center of the cyclonic action. As the Bernoulli Principle essentially states, a decrease in fluid velocity is associated with an increase in fluid pressure. It is also the principle used to work a centrifugal pump where the stator section of the casing slows down the fluid’s rate of flow after being accelerated by the impeller, converting rotational kinetic energy into the hydrodynamic energy of fluid flow.
In the case of the batea, rotational energy comes from manually spinning the batea. In Hydro-Mining rotational energy comes from the rotating rod attached to the sonic drill head and pump, circulating jetted streams of water. The sloping sides of the batea, like the sides of the mining cavity, diffuse velocity energy into pressure, generating pressure differential zones/layers. So, by manually turning the batea (generating frictional, inertial and centrifugal forces upon the batea’s contents) the slurry’s heavier material is forced outwardly and progressively downward to the batea’s apex where fluid pressure peaks to lift lighter (less-dense) material upwardly following a central vortex path to overflow out of the conical pan at the surface — making for an efficient manual way to stratify gold-bearing gravel. This demonstrates, to some degree, how Hydro-Mining is designed to work — by generating a higher, upwardly moving and more centrally oriented layer of lighter suspended material into a high, centrally oriented “vortex slurry extraction” annulus in the ceiling (aligned above the apex sump gold trap) of the mining cavity. High-pressure rotating jets intersect the upward spiraling vortex, which can possibly magnifying the effect of both the excavating jets and the vortex effect, while simultaneously using the excavating jets to generate enhanced spiraling and turbulence of the general slurry mass within the mining cavity, thereby facilitating concentration of denser slurry at the bottom apex, the sump gold trap. So, a conical batea is an established, ubiquitous, efficient slurry stratifying panning design, probably of ancient origin and tested through the ages (possibly by Solomon himself, Ecclesiastes 1:9 “… there is nothing new under the sun.”) The batea design supports modern technological advancements that reapply concepts already known to work, which in the case of placer borehole mining, describes Hydro-Mining. The circle of mining continues — the same, but better.