A variety of sampling methods exist as appropriate for the mineralization environment. Sampling aims to generate the
TABLE 7.2 A Sample Borehole Core Log Sheet
Project Name: BH No. Date of Logging
Logged by From
(m) To (m)
Core Size
Run Length (m)
Core Length (m)
% Core Recovery
Color Grain Size
Structure RQD RFM OFM VE Remarks
BH, Borehole;OFM, ore-forming minerals;RFM, rock-forming minerals;RQD, rock quality designation;VE, visual estimate.
FIGURE 7.18 The resident geologist checks the placement of each core piece to be in perfect order, carry thorough wash before logging, and sample demarcation to the best of his sincerity. His work efficiency indorse the reliability of data collection norm in mineral exploration (at Lennard Shelf camp, Australia). Any discrepancy may reject the expen- sive diamond drill hole.
best representative of the object under search (Moon et al., 2006; Dowing, 2014). Soil and rock chipping, pitting, trenching, stack, and placer sampling are practiced for surface features. Channel and chip sampling, both surface and underground, is of limited application today, but has its own merits. The diamond drill core, reverse circulation drill cuttings, and sludge collection are suitable for both surface and underground mineral exploration, and constituteþ95%
of the samples for the most reliable estimation of reserves and resources. Grab, muck, car, and bulk sampling are suitable for quick estimation of run-of-mine grade and are useful in both grade monitoring and control for blending.
7.3.1 Soil Sampling
Soil samples from residual or transported material are collected (Fig. 7.20) at a specified grid pattern designed during orientation survey. The sieve analysis of samples indicates that 80 mesh fraction of soil represents
sufficient material for further processing and provides maximum contrast between background and threshold value. The standard practice is to obtain () 80 mesh fraction for analysis of various elements.
7.3.2 Pitting
Pitting is practiced during the initial stage of surface geochemical exploration. Sampling is carried out by excavatingw11 m2pits in a rectangular or square grid pattern covering the entire target area. Pit depth varies depending on extent of weathering and nature of rocks.
The material from each meter of the vertical depth is kept in separate low-height rectangularflat stacks to determine the variation in grade and other distinctive features. Each stack represents a sample. The pits showing the presence of mineralization can be contoured (Fig. 5.2) to identify the strike and depth continuity of the orebody for drill testing.
7.3.3 Trenching
Trenches are cut across the orebody (Fig. 7.21) after the probable configuration of mineralization is outlined either by pitting or by rock/soil sampling. The sample recovered from each meter of trench is stacked separately as a sample for analysis to identify variations across mineralization. The walls of trenches can be sampled by channel cut or chip- ping for comparing with results of stack samples.
7.3.4 Stack Sampling
Stack samplingis the collection of representative broken material generated by pitting, trenching, or any mine production. The samples are collected by inserting a
FIGURE 7.20 Collection of soil sample during reconnaissance for Pte Pd target search around Tagadur chromite-magnesite open pit mine at Nuggihalli schist belt, Karnataka, India.
FIGURE 7.21 Trench sampling for platinum-group elements and chro- mite during reconnaissance survey at Sitampundi layered igneous com- plex, Tamil Nadu, India.
FIGURE 7.19 Tough bookda high-tech internet interfaced data-sharing drill core logger used at Lennard Shelf zinc deposit, Australia.
10e40 cm diameter cylinder down to the base of the stack. It is also done by collecting buckets full of sample.
A number of collection points from a stack are selected. A composite sample is prepared by a combination of one from the central part and four more from halfway between the center and corners (Fig. 7.22). Alternatively, particu- larly in the case of small pits and narrow trenches, the total recovered material can be reduced by successive crushing, coning, and quartering, and treated for chemical analysis.
7.3.5 Alluvial Placer Sampling
Alluvial placer deposits are formed by weathering, transportation, and deposition of valuable minerals. The large alluvial placer platinum deposit at the Ural Moun- tains in Russia is an example of such deposits discovered way back in 1823. In general these deposits are less consolidated, loose, and soft materials. Scooping by hand spade or the use of auger drills is employed to collect wet or dry loose sandy samples at regular grid intervals up to certain depths. A casing is driven into the deposit to protect wall collapse and avoid contamination during sample collection.
7.3.6 Channel Sampling
Channel sampling is suitable for uniformly distributed mineralization in the form of veins, stringers, and dissem- inations. Sampling is performed by the cutting of channels across a mineralized body in fresh surface exposures or underground mine workings, such as the mine face, walls, and roof. The area is cleaned to remove dust, dirt, slime, and soluble salts by any of three processes. These are
washing with a hose pipe (air/water) or scrubbing with a stiff brush or by chipping of the outer part of rocks to smoothen the sampling face. A linear horizontal channel is cut between two marked lines at a uniform width and depth (Fig. 7.23). The width is between 5 and 10 cm at a depth of 1e2 mm. Sample length varies depending on variation in mineralization. The length is preferred at a uniform unit between 1 and 2 m within mineralization to promote sta- tistical applications.
The standard tools are hammer and a sharp pointed end chisel made of drill steel, or pneumatic hammer with a pointed/chisel bit (Fig. 7.24). While the sampler cuts the channel, a second person collects chips, fragments, and fines in a clean box, sack, or on a canvas sheet spread on thefloor. A sample of 1 m length will weighw1e2 kg.
7.3.7 Chip Sampling
Channel sampling may not be representative in the case of mineralization that is irregularly distributed or dissemi- nated, and is not easily recognized by eye. Chipping fragments of w1e2 cm by 1e2 cm size covering the entire surface exposure, underground mine face, walls, and roof in a regular grid interval of 25 cm25 cm (Fig. 7.25) will be a better alternative. The area is cleaned before sample cutting. The sampler chips off fragments by
FIGURE 7.23 Schematic presentation of channel sampling of mineral exposure at surface and underground mine cross-cut wall at 1 m intervals.
FIGURE 7.24 Channel sample cut by pneumatic drill machine for exploration of platinum-group elements at open pit bench face, Boula- Nausahi chromite mine, Orissa, India.
FIGURE 7.22 Stack sampling of chromite mine production ore at Sukinda belt, India.
hammer and a pointed chisel. The chips are collected in a clean box or satchel or on a canvas sheet spread on the floor. The weight of samples from a 3 m3 m area is between 1 and 2 kg. Channel sampling is laborious, tedious, time consuming, and expensive compared to chip sampling. Chip sampling is preferred due to low cost, faster identification of mineralized contacts, and quick evaluation of grade of the area.
7.3.8 Diamond Drill Core Sampling
Diamond drill core samplingcuts/splits the core along its length into two identical halves or mirror images with respect to mineral distribution as observed during logging.
One half is grinded, reduced, and sent to the laboratory for chemical analysis. The other half is preserved in the core boxes as a primary record for future check studies. The second half can also be used as a composite sample for metallurgical test works during the initial stage of explo- ration to develop a laboratory-scale beneficiation process flow diagram. Metallurgical test work will indicate amenability, optimum grinding, liberation, and recovery leading to producing clean marketable concentrates.
A simple type of core splitter operates manually by framing a splitting unit comprising a short piece of rail foundation, with a matching chisel fitted on top and a hammer as illustrated in Fig. 7.26. The core is placed tightly between the rail and chisel, and hammered from the top to split the core into two identical halves. Hammering can be powered by compressed air. The unit is handy and low cost, and can be used in remote camp locations.
The modified form works by electric power. The cutting head is either a diamond cutting unit or a blade made of hard metal alloy (Fig. 7.27) that cuts the core into two smooth identical halves (Fig. 7.28).
FIGURE 7.26 Semimechanical core splitter used at Khetri copper mine during the 1970s.
FIGURE 7.27 Fully mechanized electric core cutter used at Lennard Shelf zinc deposit, Australia.
FIGURE 7.28 Stratiform sulfide drill core split into two identical halves by electric core cutter.
FIGURE 7.25 Chip sampling (þ) of wall/face in irregular vein-type deposits such as auriferous quartz veins.
7.3.9 Sludge Sampling
Sludge is thefiner coproduct particles of diamond drilling generated by cuttings of rocks between core and outer hole diameter.Sludge samplingforms an integral alternative in case of poor core recovery due to drilling through fractured mineralized zones. It is pertinent to recover the maximum portion of sludge in such circumstances.
Sludge collection is done in various ways as suits the operator. The simplest way is to use a plastic or metallic tub and allow the returning water to pass. The cuttings settle and can form a sample corresponding to the drilling inter- val. The method can be modified by using a large sludge box with three to four longitudinal partitions. The returning water can flow in a zigzag pattern between successive partitions so that settling of materials is improved.
Commercially designed sludge cutters with mechanical operation are available. The sludge samples are not incredibly authentic due to contamination between drill runs. However, they show the existence and to some extent the quality of mineralization in the absence of good core recovery.
7.3.10 Reverse Circulation Drill Sampling
Reverse circulation drill sampling is the collection of rock cuttings with respect to drill depth. The entire rock cuttings are raised to the surface by return air pressure and collected in glass chambers in an inverted sequence of depth (refer to Figs. 7.12 and 7.13), forming a sample.
Reverse circulation drill samples are not an exclusive and ultimate solution to mineral deposit evaluation. These samples are supported, complemented, and balanced by a certain amount of diamond drilling from a global perspective. Reverse circulation drill samples are exten- sively used in grade control of mine production in advance, and particularly for large open pit mines.
7.3.11 Grab Sampling
Grab sampling is performed at any stage of exploration, and more so during mine production for a quick approxi- mation of run-of-mine grade. The samples are randomly picked up from loose broken material from outcrops, pits, trenches, mine workings, stope drawpoints, mine cars, load shipments, and all types of stockpiles. Good care should be taken to avoid inclusion of any foreign objects like wood, iron pieces, nails, masonry, and plastics.
7.3.12 Muck Sampling
Muck sampleis composed of a few handheld spades or mechanized shovels full of mineralized fragments andfines collected from the mine face or stope drawpoints (Fig. 7.29). These samples collected from mine production
are useful to compare with drill estimates, as well as cut- tings/sludge sample values of jackhammer and long hole drills. The grades rarely match on a day-to-day basis.
However, the average production grade over a period of a week, fortnight, month, quarter, or year can be comparable depending on heterogeneity of the deposit. It also helps to indicate the intrinsic external mining dilution.
7.3.13 Car Sampling
Acar samplecomprises a handful of broken pieces picked up randomly from every 5th/10th/15th moving mine car from an underground mine (Fig. 7.30), or dumpers/trucks from a surface mine, or aerial ropeway tubs that transport ore to integrated or third-party beneficiation plants and smelters. The sample values are compared between run-of- mine and mill head grade for valuation, grade control, and reconciliation. The method is suitable for valuation of metal grade, penalty components, and moisture content of ore/
concentrate being shipped for integrated or third-party smelters.
7.3.14 Bulk Sampling
A bulk sample comprises a large volume of material (100e1000 tonnes) representing all metal grades and
FIGURE 7.29 Muck sampling collected from all sides using a handheld spade or mechanized shovel depending on the volume of the sample.
FIGURE 7.30 Car sample in underground mine by collecting a handful of ore randomly from mine cars.
mineral distributions of an entire orebody. Samples are collected from different parts of stockpiles generated from surface trial pits, underground cross-cuts, and run-of-mine ore of regular production. The best collection equipment is shovels to handle huge volumes. Total material is mixed thoroughly to reduce heterogeneity. Samples are used for developing beneficiation flowsheets for optimum reagent consumption and maximizing recovery efficiency.
7.3.15 Ocean Bed Sampling
Deep ocean floor mineral resources include polymetallic nodules, manganese crusts, active/extinct hydrothermal sulfide vents, and diamonds. They cover large areas between 4000 and 6000 m below the ocean’s surface. The polymetallic nodules contain mainly nickel, copper, cobalt, and manganese. The manganese crusts include primarily manganese, copper, vanadium, molybdenum, and platinum.
The sulfide vents contribute largely copper, zinc, lead, gold, and silver. These raw materials are found in various forms on the oceanfloor, usually in higher concentrations than in land-based mines.
Sample collection from prospective areas of the sea bot- tom is conducted by progressive reduction of sample grids through 100100, 5050, 2525, and 12.512.5 km2. The collection unit is designed as a bucket-in-pipe nodule- lifting system (Fig. 7.31), and tested successively. The quantity of materials collected in a trip isw10 tonnes and reduces to 200e500 kg.