(a) (i) What is the difference between a sample and a specimen ? (5 marks) (ii) Describe the classification of mineral reserves…

(a)(i) Sample and specimen. A sample is a representative portion of a larger body of ore, rock, coal or soil, taken by a defined method (chip, channel, core, bulk) so that its assay or test result can be applied to that body; its value lies in statistical representativeness, and it is usually crushed and consumed in analysis. A specimen is a single piece chosen because it shows a feature well (a crystal, fossil, texture or ore type) and is kept for identification, display, teaching or detailed study; it need not represent the deposit and is usually preserved intact.

(a)(ii) Classification of mineral reserves. Older Indian practice used Proved, Probable and Possible categories. Proved reserves had tonnage and grade established by closely spaced openings and drilling; Probable reserves relied on wider spacing and partly on geological projection; Possible reserves were inferred from geological evidence with little sampling.

India now uses the United Nations Framework Classification (UNFC), adopted in 2000 and made mandatory by the Minerals (Evidence of Mineral Contents) Rules, 2015. Each deposit gets a three-digit code on three axes: E (economic viability: 1 economic, 2 potentially economic, 3 intrinsically economic), F (feasibility: 1 feasibility study, 2 pre-feasibility, 3 geological study) and G (geological assurance: G1 detailed exploration, G2 general exploration, G3 prospecting, G4 reconnaissance). Reserves are the mineable part: 111 (proved) and 121/122 (probable). Remaining resources include feasibility and pre-feasibility resources (211, 221, 222) and measured, indicated, inferred and reconnaissance resources (331, 332, 333, 334). International codes such as JORC and CRIRSCO follow the same separation of resources from reserves.

(a)(iii) Marine mineral resources. They occur in several settings:

• Beach and shelf placers: ilmenite, rutile, zircon, monazite, sillimanite and garnet (Chavara and Manavalakurichi, Odisha coast), plus construction sand and lime mud on the shelf.
• Polymetallic (manganese) nodules on abyssal plains, rich in Mn, Ni, Cu and Co. India was the first pioneer investor (1987) and holds a 75,000 km² contract area in the Central Indian Ocean Basin.
• Seafloor massive sulphides at mid-ocean ridge vents (Cu, Zn, Au, Ag). India holds an ISA exploration contract (2016) on the Indian Ocean ridges.
• Cobalt-rich ferromanganese crusts on seamounts. India applied to the ISA in 2024 to explore crusts on the Afanasy-Nikitin Seamount.
• Phosphorites on continental margins, gas hydrates (Krishna–Godavari basin), offshore oil and gas, and salts and magnesium from seawater.

India's Deep Ocean Mission (2021) supports this work, and the first auction of offshore mineral blocks under the Offshore Areas Mineral (Development and Regulation) Act, 2002 was launched in November 2024.

(b) Wilfley table: principle, construction and products. The Wilfley table is a gravity concentrator. Its principle combines three effects: differential settling of heavy and light grains in a thin film of flowing water, stratification in the riffles by the shaking motion, and asymmetric (differential) reciprocation. The head motion is a slow forward stroke and a sharp return, so particles lying on the deck are moved step by step along the length. Heavy grains sink between the riffles and are carried lengthwise to the concentrate end. Light grains ride higher, are swept across the riffles by the cross-flow of wash water and leave over the lower side.

Construction:

• A rectangular or rhomboidal deck of wood or aluminium, covered with linoleum or rubber, with longitudinal riffles that taper in height towards the concentrate end.
• A small transverse (sideways) tilt of a few degrees, adjustable, towards the tailings side; the deck is nearly level along its length.
• A head motion producing about 240–325 strokes per minute with a stroke length of about 10–25 mm.
• Feed box and wash-water launder along the upper side, and discharge launders for concentrate, middlings and tailings, with slimes removed separately.

The feed must be closely sized, from about 3 mm down to about 75 µm (finer on slime tables), and the density contrast must be adequate. Tabling separates heavy mineral concentrates such as cassiterite, wolframite, chromite, native gold, ilmenite, rutile, zircon and monazite from lighter quartz and silicate gangue; it is also used to clean coal.

(c) Neyveli Lignite Mine. Neyveli, in Cuddalore district of Tamil Nadu, is India's largest lignite field and is worked by NLC India Ltd (Mine I from 1962, followed by Mines IA, II and III). The lignite belongs to the Neyveli Formation of Mio-Pliocene age (Cuddalore Sandstone), in the Cauvery basin.

• Geology: a nearly horizontal lignite seam, typically about 10–23 m thick, lies below about 70–120 m of sands, clays and sandstones.
• Groundwater problem: a confined, artesian sand aquifer lies beneath the seam. Its pressure must be reduced by continuous pumping from a ring of deep wells, otherwise the floor of the pit would heave and flood.
• Method: opencast mining with a continuous bucket-wheel excavator (BWE)–conveyor–spreader system, worked in benches. Overburden is cut in several benches by BWEs, carried on shiftable belt conveyors across or around the pit and dumped by spreaders in the mined-out area behind the advancing face (internal dumping). The lignite bench is mined separately by BWEs and conveyed to a stockyard, from where stacker-reclaimers feed the adjoining mine-mouth power stations.
• Other machinery: mobile transfer conveyors, tripper cars, dozers for conveyor shifting and bench preparation, hydraulic excavators and dumpers for difficult zones, pumps for groundwater control, and water sprinklers for dust.
• Advantages: continuous high-volume production, low cost per tonne and a short haul to the power plants. Mined-out areas are backfilled and reclaimed.