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GOLD

General Types of Auriferous Deposits

The mineralization of these particular deposits is characterized essentially by quartz; carbonate minerals, pyrite, arsenopyrite, base-metal sulfide minerals, and a variety of sulfosalt minerals. The principal gold minerals are the native metal and various tellurides; aurostibite occurs in some deposits. Characteristic types of wall rock alteration are generally developed adjacent to and in the vicinity of nearly all deposits in this class. In the old Precambrian rocks, the most common types of alteration are chloritization, carbonatization, sericitization, pyritization, arsenopyritization, and silicification. In the younger rocks, propylitization (chloritization and pyritization) is especially characteristic, and there may also be a development of adularization, silicification, kaolinization, sericitization, and more rarely alunitization.

The elements commonly concentrated in this class of deposits include Cu, Ag, Zn, Cd, Hg, B, TI, Pb, As, Sb, Bi, V, Se, Te, S, Mo, W, Mn, Fe, C02 and SiO2; less commonly Ba, Sr, U, Th, Sn, Cr, Co, Ni, and Hg and Sb are particularly characteristic of the younger deposits. The Au/Ag ratio of the ores is generally greater than 1 in most Precambrian and in some younger deposits; in many Tertiary deposits the ratio is less than 1.

Deposits of this type are widespread in the Precambrian greenstone belts of the world; Examples include Yellowknife, Northwest Territories, Canada; Red Lake and Timmins, Ontario, Canada; Kolar goldfield, India; Kalgoorlie goldfield, western Australia; and the Cam and Motor, Dalny, and other similar mines in.Zimbabwe. Younger representatives are the Mother Lode system of California (Mesozoic); Comstock Lode, Nevada (Tertiary); Goldfield, Nevada (Tertiary); Cripple Creek, Colorado (Tertiary); Coromandel gold belt, New Zealand (Tertiary); Emperor mine, Fiji (Tertiary); Lebong and other auriferous districts, Indonesia (Tertiary); Lepanto mine, Philippines (Tertiary); Kasuga mine, Japan (Tertiary), and the Belaya Gora and other similar deposits in the far eastern Russia (Tertiary).

5. Auriferous veins, lodes, sheeted zones, and saddle reefs in faults, fractures, bedding-plane discontinuities and shears, dragfolds, crushed zones, and openings on anticlines essentially in sedimentary terrains; also replacement tabular and irregular bodies developed near faults and fractures in chemically favourable beds

These deposits are widespread throughout the world and have produced a large amount of gold and silver; they are often referred to as "Bendigo type". The deposits are developed predominantly in sequences of shale, sandstone, and greywacke dominantly of marine origin. Such sequences are invariably folded, generally in a complex manner, metamorphosed, granitized, and invaded by granitic rocks, forming extensive areas of slate, argillite, quartzite, greywacke, and their metamorphic equivalents. Near the granitic bodies, various types (kyanite, andalusite, cordierite) of quartz-mica schists and hornfels are developed and grade imperceptibly into relatively unmetamorphosed slates, argillites, quartzites and greywacke marked by the development of sericite, chlorite and other low-grade metamorphic minerals. Most of the gold deposits are developed in the lower-grade facies. A few economic deposits occur in the granitic batholiths and stocks that invade the greywacke-slate sequences.

The principal gangue mineral in these deposits is quartz; feldspar, mica, chlorite, and minerals such as rutile are subordinate. Among the metallic minerals, pyrite and arsenopyrite are most common, but galena, chalcopyrite, sphalerite, and pyrrhotite also occur. Molybdenite, bismuth minerals, and tungsten minerals are local. Stibnite occurs in abundance in a few deposits, but is relatively rare in most deposits. Acanthite, tetrahedrite-tennantite, and other sulfosalts are not common in these deposits. Carbonate minerals, mainly calcite and ankerite, are common but not abundant. The valuable ore minerals are native gold, generally low in silver, auriferous pyrite, and auriferous arsenopyrite. Telluride minerals are relatively rare, and aurostibite is an uncommon mineral in these deposits.

A few deposits in this category are tabular or irregular replacement (disseminated) bodies developed in carbonate rocks or calcareous argillites and shales. The principal minerals in these deposits are quartz, fluorite, pyrrhotite, pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, and stibnite.

As a general rule, wall rock alteration associated with these deposits is minimal, and the quartz veins, saddle reefs, and irregular masses are frozen against the slate, argillite or greywacke wall rocks. In places, thin zones of mild chloritization, sericitization, and carbonatization are present. Some veins are marked by thick black zones (up to 15 cm wide) of tourmalinized rock. Disseminated pyrite and arsenopyrite are common in the wall rocks of most of these deposits. This pyrite and arsenopyrite is usually auriferous.

The elements exhibiting a high frequency of occurrence in this type of gold deposit include Cu, Ag, Mg, Ca, Zn, Cd, (Hg), B, (In), (Ti), Si, Pb, As, Sb, (Bi), S, (Se), (Te), (Mo), W, (F), Mn, Fe, (Co), and (Ni). Elements in parentheses have a low to very low frequency of occurrence. The Au/Ag ratio in the ores is generally greater than 1.

Deposits in essentially sedimentary terrains are widespread throughout the world. In Canada, Examples occur in the Archean Yellowknife supergroup in the Yellowknife district, Northwest Territories (Ptarmigan, Thompson-Lundmark and Camlaren mines); in the Paleozoic Cariboo group at Wells, British Columbia (Cariboo Gold Quartz mine); and widespread in the Ordovician Meguma group of Nova Scotia. Elsewhere in the world deposits of this type occur in the auriferous Appalachian "Slate Belt" of the United States (Paleozoic); Salsigne mine, Montagne Noire, France (Paleozoic); Sovetskoe deposit, Yenisey region, Russia (Proterozoic); Muruntau deposit, Uzbec Russia (Paleozoic); Bendigo deposits, Victoria, Australia (Paleozoic); and the Pilgrims Rest and Sabie goldfields in the Transvaal System, South Africa (Proterozoic?).

6. Gold-silver and silver-gold veins, lodes, stockworks, and silicified zones in a complex geological environment, comprising sedimentary, volcanic, and various igneous intrusive and granitized rocks

Deposits in this category combine nearly all the epigenetic features described in categories 4 and 5. Quartz is a predominant gangue, and some deposits are marked by moderate developments of carbonates. The orebodies constitute principally quartz veins, lodes, and silicified and carbonated zones. The gold is commonly free but may be present as tellurides and disseminated in pyrite and arsenopyrite. The Au/Ag ratio of the ores is variable depending upon the district and often upon the deposit.

http://amazingrust.com/experiments/how_to/Images/H2SO4_Density_Table.jpg

the page images and searchable text from a 1932 United States Geological Survey report on the gold-bearing formations of the Alleghany district, in the southern part of Sierra County, California. The district is known for the high-grade gold ore of its quartz veins, which between the 1850s and 1930 yielded $20 million, and now-rare lode mining continues there today.

USGS Professional Paper 172 expanded upon the Colfax and Downieville folios of the Geologic Atlas of the United States, published 30 years earlier. The report updated the descriptions, made by Waldemar Lindgren in the Colfax folio, of three quartz formations, and it identified two additional gold-bearing formations. After a general discussion of area geology, the report details and maps mineralogy, origin of deposits, and the key lode mines and prospects of areas draining to Oregon Creek, Kanaka Creek, and the Middle Fork Yuba River. Graphics include photographs of quartz and mineral samples, colorful general and local geologic and topographic maps and sections, and intricate drawings of the tunnel networks of the largest mines.


Contents:

Outline of the report

Part 1. Geology
Introduction
Scope of the report
Location and topography
Field work and acknowledgments
Previous work Rock formations
“Bedrock series”
Blue Canyon formation
Tightner formation
Kanaka formation
Areal extent
Conglomerate member
Lower slate and greenstone member
Chert member
Upper slate and greenstone member
Sections
Relief quartzite
Cape Horn slate
Serpentine
Gabbro and diorite
Quartz diorite
Granite and aplite
Age of the “Bedrock series”
“Superjacent series”
Early gravel
Intervolcanic gravel
Andesitic breccia
Basalt
Pleistocene and Recent gravel Geologic structure and history
Structure of the “Bedrock series”
Faulting
Tertiary history
Development of the present topography

Part 2. Ore deposits
History and production
The veins
Scope of descriptions
Distribution
Relation to country rock
Size and structure
Mineralogy
Summary
Chlorite stage
Quartz stage
Arsenopyrite and pyrite
Quartz
General features
Vacuoles
Plagioclase
Barite
Chalcedony
Carbonate and sericite
Apatite
Beidellite
Carbonate stage
Character of mineralization
Carbonate
Mica (mariposite and sericite)
Chlorite
Talc
Carbon (graphite)
Palygorskite
Rutile
Quartz, chalcedony, and opal
Sulphides
Gold
Final stage
Oxidation
Oreshoots
Character
Productivity of veins of different types
Favorable structural features
Mineralogic indications
Probable persistence in depth
Origin of the deposits
Age of the veins
Depth of vein formation
Origin of the fissure systems
Pressure and temperature
Source of the minerals
Possibility of derivation from the wall rock
Minerals of the chlorite stage
Quartz and carbonate
Arsenopyrite
Mariposite
Chromite
Gold
Graphite
Plagioclase
Barite
Method of vein formation
Chlorite stage
Quartz stage
Possible recrystallization
Replacement
Fissure filling
Conclusions
Carbonate stage
Summary

Mine descriptions
Mines of Oregon Creek drainage basin
Brush Creek mine
Finan prospect
Kate Hardy mine
Hardy Kate prospect
Tomboy prospect
Eureka mine
Oak prospect
Mugwump mine
Gold Bug prospect
Federal mine
South Fork mine
Amethyst mine
Diadem mine
North Fork mine

Mines of Kanaka Creek drainage basin
Kenton mine
Roye-Sum prospect
Oriental mine
Frances D prospect
Spoohn mine
General Sherman prospect
Wyoming group (Dead River)
Wonder prospect
Rainbow mine
Rainbow Extension mine
Sixteen to One mine
Ophir mine
Eclipse mine
Morning Glory mine
Extension of the Minnie D mine
Minnie D and Lucky Larry mines
Osceola mine
Panama prospect
Red Star mine
Rao prospect
Mayflower prospect
Mariposa mine
Central mine
Snowdrift prospect
Eldorado mine
Yellow Jacket (Colorado) mine
Eastern Cross group
Rising Sun mine
Iroquois prospect
Dreadnaught mine
Belmont prospect
Golden King mine
Docile mine
Continental mine
Mammoth Springs mine
Kinselbach (Acme) mine

Mines in the drainage basin of the Middle Fork of the Yuba River
Mountain View prospect
Maryland prospect
Oriflamme mine
Irelan mine
Arcade mine
Cooper prospect
Plumbago mine
German Bar mine
Gold Canyon mine
Independence mine
Future of the district

Plates

Geologic map of the Alleghany district, California
Crumpled hornblende schist of Tightner formation between Morning Glory and Osceola mines
Slate of the Blue Canyon formation, near Mammoth Springs mine
Crumpled hornblende schist, siliceous facies of Tightner formation, valley of Kanaka Creek
View from Alleghany, looking down valley of Kanaka Creek
Geologic Map of the region surrounding the Alleghany district
Hornblende schist with streaks of quartz, Tightner formation, near lower Osceola tunnel
Basal conglomerate (tillite?) of Kanaka formation near transformer house, Alleghany
Chert of Kanaka formation, South Fork of Yuba River near Washington
Detail showing contorted banding in chert, South Fork of Yuba River near Washington
Relief quartzite, fold in quartzitic slate, Kanaka Creek near Rapps Ravine
Typical exposure of serpentine, nearly bare of vegetation, valley of Kanaka Creek
Eocene gravel at old hydraulic workings south of Alleghany
Flows of Pleistocene basalt capping Miocene andesitic breccia, Bald Mountain
Map showing location of fault east of Alleghany with reference to the Mother Lode system
North side of valley of Kanaka Creek looking toward Sixteen to One mill, showing shoulder below lava
Outcrop of vein on footwall side of Sixteen to One vein
Junction of Sixteen to One vein and vein along steep fault
Principal fissures of the Alleghany district, projected to plane of 3,700-foot contour
Map of the Alleghany district, showing principal mine workings and mining claims
Structure sections through the eastern part of the Alleghany district In pocket.
Vein with septa of altered country rock separating quartz strands, North Fork mine
Junction of main vein and fault vein, Sixteen to One mine
Altered but unsheared country rock separating quartz strands, Rainbow mine
Banding in vein due to shearing, Sixteen to One mine
Quartz stringers in footwall of vein, Eldorado mine
“Crossover” stringers between hanging wall and footwall, Kate hardy mine
Vein with sharp footwall due to faulting and frozen hanging wall with quartz stringers, Plumbago mine
Quartz stringers in altered slate close to main vein, Rainbow mine
Lenses of quartz in crushed slate along wall of Clinton veils, Rainbow mine
Lenses of quartz and carbonate in crushed slate, Kate Hardy mine
Quartz stringers cutting Cape Horn slate, Brush Creek mine
Breccia containing quartz fragments, cemented by fine-grained quartz, along hanging wall of vein, Eldorado mine
“Headcheese” breccia, Eldorado mine
Vein with well-marked “walls,” Plumbago mine
Walls of vein due to postmineral movement, Plumbago mine
Footwall of vein marked by curving fault, Plumbago mine
Fault plane passing from footwall to hanging wall of vein, Sixteen to One mine
Quartz displaced by minor fault, Eldorado mine
Wedge of quartz bounded by faults, Oriental mine
Specimen of ribbon quartz, German Bar mine
Ribbon quartz with bands parallel to walls, Sixteen to One mine
Ribbon quartz cut by transverse sheeting, Kate Hardy mine
A, Junction of Oriental and Alta veins, Oriental mine
Vein with lower strand showing crinkly banding and strand above containing wall-rock inclusions, Eldorado mine
Development of chlorite and albite in saussuritized gabbro
Grain of chromite in serpentine veined by antigorite
Vein quartz showing inclusions associated with septa of country rock
Vein quartz with abundant inclusions
Arsenopyrite veined by quartz and crystalline against quartz, with gold replacing arsenopyrite
Arsenopyrite broken and veined by quartz, with gold for the most part replacing quartz
Pyrite veined by quartz
Pyrite veined by quartz which shows clear border
Quartz grain showing crystal faces surrounded by quartz with allotriomorphic texture
Quartz crystal with core containing abundant vacuoles, surrounded by growth of relatively clear quartz
Same as D, with crossed nicols
Vein quartz showing rosette of outward-pointing quartz crystals
Quartz crystals normal to face of arsenopyrite crystal
Quartz crystals elongate normal to wall of vein
Quartz veinlet with cross-fiber structure
Samite as B, with crossed nicols
Vein quartz showing strain twinning and microbrecciation
Quartz crystal showing vacuoles in zones parallel to prism with grain boundary due to later fracture
Same as E, with crossed nicols
Cloudy quartz cleared in zone of microbrecciation
Same as A, with crossed nicols
Change in grain close to wall of vein, probably due to later fracturing
Same as C, with crossed nicols
Albite, dark from abundance of vacuole inclusions, intergrown with quartz
Same as A, with crossed nicols
Detail of A, showing contact of quartz and feldspar
Albite with zoning due to vacuoles
Intergrown quartz and albite showing vacuole inclusions
Vacuoles with gas bubbles in quartz
Inclusions in quartz—clusters of minute inclusions and negative crystals with bubbles
Quartz crystal showing zonal structure due to arrangement of vacuoles
Complex zoning in quartz due to vacuole inclusions
Same as A, with crossed nicols
Quartz grain showing crystal boundaries and core containing abundant inclusions
Quartz crystals elongate normal to wall of vein, crossed by lines of vacuoles
Same as D, with crossed nicols
Lines of vacuoles crossing quartz grains
Linearly arranged vacuoles
Relation of vacuoles to strain twinning
Same as C, with crossed nicols
Lines of vacuoles radiating from sulphide
Granite altered to fine-grained albite
Tubes in quartz radiating out from carbonate
Minute tubes in quartz
Quartz crystal showing twinning in inner and outer zones
Vein of albite crossing older albite crystal
Zonal distribution of sericite in quartz crystal
Detail of A
Original albite of granite veined by quartz and later albite
Spherule of chalcedony in quartz
Zoned carbonate replacing albitized granite
Quartz replaced by chlorite and two generations of carbonate
Early arsenopyrite veined by quartz and fringed by crystals of later arsenopyrite
Same as D, with crossed nicols
Breccia of quartz fragments cemented by carbonate
Fault breccia containing quartz fragments with matrix of mariposite and ankerite
Microbrecciated quartz replaced by carbonate
Saussuritized gabbro replaced by chlorite and albite, with later development of carbonate and chlorite
Mariposite in parallel arrangement in quartz
Rutile in oligoclase
Botryoidal talc replacing quartz
Detail of C, showing contact of talc and quartz
Veinlet of later quartz with opal and chalcedony
Same as A, with crossed nicols
“Headcheese” breccia
Veinlet of clear quartz cutting strain-twinned crystal of older quartz
Same as A, with crossed nicols
Vug filled with opal amid chalcedony
Veinlet containing quartz, chalcedony, and opal cutting opalized granite
Veinlet of later quartz crossing area of microbrecciation
Same as A, with crossed nicols
Veinlet of later quartz with carbonate
Opal containing metallic mineral
Later arsenopyrite fringing earlier
Gold in breccia with opal cement
Opal replacing albitized granite
Pyrite replaced by tetrahedrite
Jamesonite crystals in vug
Needles of jamesonite in quartz
Arsenopyrite along crenulations in quartz
Gold and galena replacing quartz in contact with coarse arsenopyrite; B, Crushed arsenopyrite fringed by gold
Gold replacing fractured quartz
Gold in quartz and carbonate
Specimen showing crinkly banding
Map of a portion of the Sierra Nevada showing major features of Tertiary drainage
Crinkly banding in quartz with later microbrecciation
Crinkly banding with texture suggesting recrystallization
Sericite band crossing single quartz grain
Folded septum of slate between quartz strands
Crinkly banding crossing strain-twinned quartz
Zoned lamellar quartz crystals
Arsenopyrite veined by quartz with growth of quartz crystals outward from face
Fragments of arsenopyrite in quartz
Clustered arsenopyrite crystals veined by quartz
Geologic map of Kate Hardy mine
Sketch map of South Fork, Mugwump, and neighboring mines
Geologic map of vicinity of Oriental shaft
Geologic map of Oriental mine
Geologic sections, Oriental mine
Map of workings of Rainbow mine, Rainbow Extension mine, and Spiritualist tunnel
Map of Sixteen to One mine
Map of workings of Morning Glory, Extension of Minnie D, Minnie D, Lucky Larry, and Eclipse mines
Map of Yellow Jacket, Eldorado, and neighboring mines
Map of workings on Eldorado vein, Eldorado mine
Map of Irelan mine
Map showing principal workings of Plumbago mine

Figures

Map showing location of the Alleghany district, California
Sketch map of outcrops along the Middle Fork of the Yuba River near Jackass Ravine
Section along prospect tunnel south of Irelan mine
Granite dike cutting schistose gabbro, French Ravine
Gold produced from lode and placer mines of the Alleghany district, 1891-1927, and ore mined, 1903-1927
Details of junction of main vein and fault veins, Sixteen to One mine
Map of western part of adit level, Oriental mine
Section showing detail of junction of Sixteen to One and Ophir veins, Sixteen to One mine
Section along vein in Eldorado mine
Sketches showing thrusting in veins
Sections across vein, Plumbago mine
Plan and sections of a part of the Rainbow mine, showing relation of Rainbow and Clinton veins
Section of Sixteen to One vein below drain tunnel
Arsenopyrite veined by quartz
Radiate needles of galena, probably replacing jamesonite
Gold and galena in arsenopyrite
Gold replacing quartz and arsenopyrite
Sketch of Gold Canyon vein, showing occurrence of arsenopyrite and gold
Sketches showing relation of crinkly banding to ribbon quartz
Sketches showing possible folding of vein quartz
American tunnel, Brush Creek mine
Drifts from winze, Brush Creek mine
Sketch map of Finan prospect
Surface geology, Kate Hardy mine
Map of lower tunnel, Tomboy prospect
Sketch map of workings, Oak prospect, Bob Evans claim
Plan of workings of North Fork mine and section along line A—B
Sketch map of accessible workings of Kenton mine
Map of General Sherman tunnel
Plan and section of parts of the 900-foot, intermediate, and 1,000-foot levels, Sixteen to One mine
Map of Ophir mine and adjoining workings of Sixteen to One mine
Map of drain level, Ophir mine
Map of upper tunnel, Extension of Minnie D mine
Map of workings, Osceola mine
Map of workings, Red Star mine
Sketch map of Mayflower prospect
Plan of Dreadnaught tunnel
Map of workings, Docile mine
Sketch map of lower tunnel, Mammoth Springs mine
Sketch map of Mountain View tunnel
Sketch map of Oriflamme tunnel
Sketch map of upper tunnel, Arcade mine
Sketch map of lower tunnel, Arcade mine
Map of Plumbago mine
Map of German Bar mine
Map of Gold Canyon mine
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Gold in arsenopyrite or high-arsenic pyrites commonly exists as submicroscopic or “invisible” inclusions, making it refractory to cyanide leaching. Current practice favour an oxidising roast to liberate the gold for cyanidation because it is fast and energetically self supporting. However, the SO2 gas it produces can create a handling problem. One alternative we are investigating is pyrolysis under N2, CO2 and SO2 atmospheres. Instead of gaseous SO2, the process produces elemental sulfur and, if present in the ore, arsenic metal or solid arsenic oxide. Pyrolysis experiments were conducted on a gold-containing refractory arsenopyrite ore to determine the effect of temperature, time and atmosphere on the cyanidation characteristics of the pyrolysis product. In N2 and CO2, the ore behaved similarly, reaching maximum mass loss at 700°C and yielding maximum gold recoveries of 35 and 48 %, respectively. Pyrolysis under SO2 was faster, reaching maximum mass loss at 600°C and resulting in gold recoveries of up to 61%. The low gold recovery for N2 and CO2 pyrolysed products was due to the encapsulation of the exsolved gold particles by pyrrhotite as it recrystallised during the process. All the pyrolysis products, although composed mainly of pyrrhotite, did not seem to be highly active in cyanide solutions.
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from wikipedia
Gold extraction

Sodium thiosulfate is one component of an alternative lixiviant to cyanide for extraction of gold.[3] It forms a strong complex with gold(I) ions, [Au(S2O3)2]3−. The advantage of this approach is that thiosulfate is essentially non-toxic and that ore types that are refractory to gold cyanidation (e.g. carbonaceous or Carlin type ores) can be leached by thiosulfate. Some problems with this alternative process include the high consumption of thiosulfate, and the lack of a suitable recovery technique, since [Au(S2O3)2]3− does not adsorb to activated carbon, which is the standard technique used in gold cyanidation to separate the gold complex from the ore slurry.
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Patent # 3,957,505

I have attached the pdf of the patent for easy familiarization.

US3957505.pdf


1. A process for extracting gold from gold bearing material which comprises:
treating the gold bearing material in an aqueous solution consisting essentially of iodine and a water soluble iodide salt to dissolve gold from said gold bearing material; mixing a reducing agent with said aqueous solution to reduce dissolved gold iodide salts to gold metal and precipitate said gold metal in substantially pure form from said aqueous solution; Removing precipitated gold metal from said aqueous solution; and adding an oxidizing agent to said aqueous solution to thereby restore said solution to substantially its original condition for dissolving gold from further gold bearing material.
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Recovery of Gold in Pyritic Sulfide Ores

The now extinct Us Bureau of Mines conducted numerous studies of gold in pyrite, and sulfide ores over the years, until their untimely demise in the 1990's. Much of the referenced studies and case applications discussed in this brief article came from USMB reports, which even after they ceased to exist, still continue to provide some good scientific information to those working in the mining and mineral processing industries.

Sulfide ores, and pyrites in particular, have caused and continue to cause difficulty in recovering the gold values from these ores. In most instances, visible gold can not be seen under microscopic examination of pyrite gold ores. However, if the ore is ground to -200 mesh, most times, a few specs of gold can be visibly seen under microscopic examination. Based upon numerous case studies, it appears that gold particles in pyrite are generally fine, ranging from 75 microns down to 2 or 3 microns. The incidence of fine gold's quantity also appears to be related to the gold concentration, as well. If the assay is 2 ounces per ton, there are generally larger gold particles present along with the typically fine micron sized gold. When the grade diminishes to say, 0.2 ounces per ton, there are generally only micron sized particles associated with the pyrites in the ore. This is not absolute, but it does appear to be the trend.

Recovery of gold in sulfide ores has fallen into several categories. First is froth flotation, and second is cyanidation of the ores. Using cyanide to recover gold from sulfide ores generally results in 30 to 35% recovery, and the best I have heard of is around 50% recovery. The fine coating of a iron compound definitely appears to be a key component of the inability of cyanide to efficiently leach low grade pyritic ores. Perhaps there is some room here for a pretreatment, to remove this iron coating and then make the fine particles susceptible to cyanide leaching. To my knowledge, this has never been attempted. Generally speaking, cyanide leaching of low grade pyritic ores is economically unsatisfactory in today's market.

Low grade ores that do not respond well to cyanide or flotation are generally referred to a "refractory" ore. Which usually means that it needs to be roasted to release the gold. Roasting has to be one of the most expensive methods of recovering gold with current environmental considerations, and is usually cost prohibitive, except in a few circumstances, where grade and volume justify the economics.

Gravity concentration tends to recover the pyrite with the gold, and only removes the lighter minerals, such as quartz, from the ore. The most difficult particles to gravity concentrate are the fines, and 75 microns to 2 microns are definitely very fine. So, even if the ore were ground to 2 microns, it may not be recoverable using current gravity technology.

That appears to leave froth flotation as still the best method of recovering the gold from pyritic ores. Sulfide ores, such as chalcopyrite, sphaelerite, galena, and pyrrhotite, and mixtures of these ores have historically been found with micron size gold particles included in them. This generally involves frother, several collectors (promoters) and possibly some modifying or depressing agents as well.

Geologists and mineralogists have many theories why and how the gold occurs with the pyrite, and I will not enter into any of these areas, since I am concerned with liberating the gold from the ores. I will say that from my understanding, many seem to agree that in sulfide gold ores, the occurrence of gold appears to occur as a replacement of other minerals, possibly iron. One USBM paper summed up five noticeable characteristics of auriferous pyritic ores. The gold occurs as tiny flakes on the crystallographic planes of the pyrite. The gold flakes are very small in size, 5-10 microns. The pyrite in which small amounts of gold occurs is of crystalline variety (primary pyrite). The characteristics of primary pyrite are a absence of porosity, an extreme brittleness, a resistance to oxidation, and the existence of gold possessing a weak susceptibility to magnetism (due to a fine coating of a iron compound).

My theory is that if some economical pre-treatment in a heap leach situation, could nullify the effects of the iron coating, chemically, then the pyritic ore could be effectively and economically leached with cyanide in the heap leach. This would make the recovery of gold from pyritic sulfides economical, and negate spending hundreds of millions of dollars on roasting plants. But in the end, it all comes down to cost, which would be the most cost effective. We know roasting is almost prohibitively expensive, so I would think that treating in a heap leach, prior to cyanidation, would be much more cost effective.

Charles Kubach, Mining & Mineral Processing Engineer
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Thanks grolic added this one to the gold folder. gypsy Thank you. I have seen the gold hunter kit on the web. It was used in a demontration video on youtube of guy macking a small BB of gold {cool^sign}
Here is what I found somewhere. I know it is incomplete. It's the first line that hooked me.
Yes, the clorox and water leach solution is good to get stated with as clorox is readily available.

Clorox is based on 6% sodium hypochlorite which in the powder form is the pool chemical used to keep a
slight residual of chlorine Cl2 in the pool water as a disinfectant. Clorox in the bottle also has sodium
hydroxide NaOH added to keep the solution alkaline and thus keep the chlorine from gassing off.
Dilute the clorox with water, upsets the alkalinity and drives the solution pH toward being less alkaline
and toward acidity, but not much. Just enough to release some free chlorine. It is the chlorine that dissolves
the gold as AuCl4H. Usually as the chlorine is used up, more chlorine is freed up to dissolve more gold

Cannot begin estimate how well the clorox leach will work on your black sands since it is so weak. And there
may be other metals which take up the chlorine. Thus we move ahead a bit and soak the black sands in a
50:50 solution of hardware store muriatic acid (HCl) concrete cleaner to remove as much iron, etc. as possible.
After leaching with the muriatic acid for 4 - 8 hours or even longer, we pour off the muriatic acid with the
leached unwanted iron and any other metal, neutralize the solution and dispose of it. Also wash the remaining
sands a few times with clean water to remove any residual metal laden acid solution.

Now we are ready to leach and should have better leaching with the clorox and water leachate.

Or we can move ahead again since we have the muriatic acid concrete cleaner and use this leachate which will
be an acid leach with much more free chlorine. 4 parts muriatic acid plus 1 part clorox for a total of 5 parts.
Now we are cooking with a stronger leachate and stronger chlorine smell coming off the leachate. As the free
chlorine is used up, more free chlorine will go into the solution to eat up the gold. But since we are not going
to have very much gold in the black sands, this leachate works faster - 4 - 8 hours or less at room temperature.
We have to stir the pot occasionally to provide good mixing. Tight fitting lid on a 2 gals plastic pail is good to
use for safety reason and keep the chlorine gas confined. Strong puff of chlorine though when the lid is taken off!

Okay, with the lid off so we don't disturb the solution mix, let the solids settle. Then pour off (decant is the word)
the solution to your Pyrex or whatever pot. Let the leaching solution settle again and then pour off the remainder
to your pot. Idea is to settle and decant as much solution without filtering all the sludge.

Now important step. When playing chemist, NEVER throw out anything because the method can and does go wrong.
Put the black sand sludge aside as it contains any silver, platinum, palladium or other platinum group metals if we are interested.

Now the decanted solution may be cloudy and we want the solution to be a clear as possible. We can just set it aside for
a day and let the fines settle to the bottom which is what I do, and then decant the clear solution again. If the solution
with our gold in it will not clear up, we can filter it through 3 - 4 coffee filters but they are quite coarse and may not
clear the solution. So we move on to getting the gold (if it is in the solution).

We take a cup of the solution and heat it up to about 60 deg C (140 F) and add some ferrous sulphate lawn fertilizer to
it by dribbling from a teaspoon. Plastic spoon is okay. The ferrous sulphate is brown. If the hot solution clouds up to a
muddy brown and a brown powder settles to the bottom of the glass container, we have gold!

Now we won't waste our time and fertilizer on the remaining solution in the Pyrex coffee pot. We heat that solution to
the same temperature, dribble in the ferrous sulphate until all the gold is precipitated when the solution no longer clouds
up and then set the pot aside to cool and settle the remaining gold to the bottom of the container overnight.

Next day we decant the clear solution off the brown gold powder without losing any gold powder, then wash the gold
powder with clean water which clouds up and must be left to settle out the gold again. After the gold settles again
we decant the clear water off the gold. Then let the remaining gold powder air dry or over very low heat until dry.
Do not use too much heat or the gold powder will stick to the Pyrex pot bottom and be hard to scrap off! Air dry is better.
We can then brush the gold powder with a small soft brush like a cosmetic powdering brush into a pile and dump it
into our collection container.

One can filter the brown gold powder through 2 or 3 coffee filters but if a small amount of gold powder it will get lost
on the filter paper. Large amounts of gold powder can easily be filtered using the coffee filters. And left on the filters until
the day we put them into a graphite crucible and with the torch and flux, get our gold bead.

Can things go wrong, Of course and that why we don't throw anything away while we make adjustments or think
about what went wrong. Is it tedious work? Yes, work that only a chemist can love because of the magic and alchemy
of a little bit or this and a little bit of that all mixed together without an explosion or bad smell is very rewarding!

In your No 5 step we don't filter the remaining liquid fraction after precipitating the gold. There is nothing to filter.
Neutralization should not be necessary, only use dilution - plenty of water discard the bleach.
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Black sand gold recovery

"WORKING BLACK SAND and SULFIDES in GOLD RECOVERY"

Heres How You Do It

Getting upto 90% of your Sulfide Gold out of the Black Sand Concentrates

1,[FOR STARTERS] What you'll need to process Black Sand Concentrates. one #12 classifier... one #20 classifier... two gold pans... water... wash tub.... few 5 gallon buckets... micro sluice or gold wheel... tumbler andKeene Gravity Bowl...

2, Your first few steps. Classify your material into several sizes... Larger than # 12 [nugget size, you can pick'em out]... Larger than # 20 [micro sluice/gold wheel or you can pan this out, it's really easy]... Smaller than # 20 [this is for your tumbler]...

3,Put the smaller than #20 concentrates into your tumbler... Add acidic acid "cider vinegar" or Citric acid "stronger"and tumble over night... Take concentrates "the tumbled stuff" when done flush brown mud "dissolved iron" with water and add cons using a small scoop into a running KGB BOWL... Once finished running the KGB, snuffer out the fine Gold... Take the remaining Black sand "left in the KGB" and mix it with equal amounts of Table salt... Put the mixed product into an iron skillet... heat up untill completely dry "do this outside"... Once really hot and dry, pour the mix into a tub/bucket of cool water... "DON'T PUT THE IRON SKILLET INTO THE WATER" Just dump the sand/salt "this fractures the attached Gold"... Collect up the stuff you just dumped into the cool water... Now run this material thru your KGB gravity bowl... Snuffer up the visible gold when done...

4, What did I just do, you ask... You classified your material by size "largest to smallest"... If you have the necessary equipment "you just eliminated 99% of the panning your concentrates"... By tumbling the smallest size with vinegar "you just cleaned it up and removed the organics" and much of the iron... By roasting it, "you fractured the sulfide Gold and attached gold from the black sand"...

5, Is it worth it ??? YOU BET IT IS... Most of the time there is 4 - 10 times more ulta-fine "Micro Gold" in your Black sand than Visible Gold... Gold is Gold Reguardless of it's size, oh sure the big stuff is great !!! But that Fine Gold really can start to add up and do it quickly...

You can go even further and get the really fine invisible micro gold out also. But that gets involved using some basic chemistry and several more steps and some additional time and expense.

"IF YOU TAKE THE EXTRA TIME AND STEPS TO RECOVER IT"...

article courtesy of nuggethunters.org

................................... More tips for removing fine gold from black sands.

I know a couple of fine-gold tricks: Add a little CLR (from Home Depot)to your black-sand cons and swish it around and let it sit for about a week. Pour off the CLR and rinse the cons with fresh, clean water and recheck for "gold". Also, I've heard you can dry the cons, add table salt and cook it in the open air (don't be breathin' Mercury!) and this will sometimes bring out the flour gold. "Lick" your dry finger and touch the flour gold. It'll stick--then put your finger over a water-filled recovery vial and shake it. Bingo--you've got that piece!

...................................

The secret to panning the micron-fine colors the old-timers called "dust" (now called "flour" gold) is to (1) Periodically for about a week, shake the cons in a glass jar to which some white vinegar and salt have been added, to clean the colors. (2) Screen the cons through -20, -50, -100, and -230 classifiers and process the lots separately. (3) Use a magnet wrapped in a baggie to carefully remove the magnatite particles from the cons. This will reduce the bulk of the cons by up to 50%. (4) SLOWLY & CAREFULLY pan each lot of non-magnitic particles in a controlled water environment to which a few drops of "Jet-dry" or good grease cutting liquid dish detergent has been added, to keep the colors from floating. (Cont'd)



Get the colors to the bottom of the pan and VERY GENTLY rinse the sands back on the bottom. Use quick "taps" on the edge of the pan to move the colors futher away from the sands. (5) Suction the colors and remaining sand particles into a sniffer/sucker bottle and then spread them out on piece of tinfoil and let them thoroughly dry. (6) Use you mouth to gently blow the remaining black sands away. (7) Bend the foil into a "v" & tap the sides so the colors fall down into the vortex, then tap and pour the colors into a vial. Good luck.
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