collapse


* User Info

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Who's Online


Dot Guests: 173 | Dot Users
Dot Hidden: 0

* Board Stats

  • stats Total Members: 12501
  • stats Total Posts: 124059
  • stats Total Topics: 17149
  • stats Total Categories: 5
  • stats Total Boards: 48
  • stats Most Online: 814

* Advertisers

Author Topic: Placer Deposits  (Read 10641 times)

0 Members and 1 Guest are viewing this topic.

Offline GPEX admin

  • Administrator
  • **********
  • Posts: 2070
  • Province/State: Hope, BC Canada
  • Country: ca
  • Kudos: 47
  • Larry
    • GPEX Gold And Platinum Explorations
Placer Deposits
« on: January 27, 2008, 01:50:18 PM »
PLACER DEPOSITS

Placers are deposits of sand, gravel, or other alluvial material which contain particles of valuable minerals in workable quantities. In addition to the occurrence’ of gold in placers, other valuable minerals such as platinum, cassiterite (tin ore), silver, copper, rubies, and diamonds may also be found in placers.

There are two general types of placer deposits: (1) Residual placers and (2) transported or alluvial placers. In both types, the source of the gold was originally in lode or Vein deposits in solid rocks, the gold being eventually freed from its enclosure rock by the action of changes in the elements (changes in temperature, frost, rain, wind, chemical actions) gradually decomposing and partially removing some of the rock by mechanical means or in solution.  In the case of residual placer deposits, which are comparatively unimportant as a source of placer gold, the gold and much of the decomposed vein-rock is left in approximately its original location.

Transported placers, also derived by the weathering of lode and vein deposits of gold, result from the removal of the decomposed gold-bearing rock by natural agencies, principally running water, and the further crushing and breaking of the rock during the period of travel, by the action of solution and abrasion, which in turn is followed by the sorting action of the moving water which carries away the lighter and finer material and permits the deposition of the heavier materials, including the gold and black sands, at places in the Stream where the velocity (speed) of the moving mater is reduced. The largest and heaviest pieces will obviously be deposited first, or nearest their origin in the lode or vein, while the lighter and finer material will frequently be carried long distances.

Due to the different amounts of material which will flow in any stream, during the course of many seasons, the gold, black sands, and rock material deposited in the stream-bed will be re-sorted and worked over many times until finally the gold, black sand. and other heavy particles become concentrated at or near bed-rock of the creel-bottom. After the gold reaches bed-rock, the gold, black sand or a clay or hard-pan false bed-rock, it may be moved slowly down-stream until it lodges in crevices, cracks, or other irregular openings in the bed-rock.

There is no fixed rule as to where gold is apt to occur in the stream-bed, as the velocity of the stream is not the same at all points and the gold is naturally dropped by the water to the stream-bottom when the velocity of the water is not sufficient to carry it along. At the time of formation of transported placer deposits, water was necessarily present, but later disturbances, geological changes and erosion, changes in the Stream-course, or changes in the climate may have caused the stream to flow in a different location or to dry up, thus leaving the placer deposit high up on the bank of a stream or in a dry location. Streams are often found to have a bed of clay or hard-pan on or above the true bedrock. This layer of clay is known as a false bed-rock and it may have a marked effect on the distribution of the gold in the placer. Clay and hard-pan form impervious beds on which the deposition of gold may take place, and while they act as concentrating horizons in the stream-bed, it does not mean that gold will not be found below them on lower horizons, for the gold might have been deposited lower down in the stream-bed before the clay and hard-pan beds were formed.

To distinguish between the many types of transported placers, the following are some of the terms used to describe the most commonly encountered types :

Creek Placers - These are gravel-deposits found in the beds and intermediate flood-plains of small streams. They are generally shallow and have been the most productive of high-grade placer gold, the gold generally being concentrated on or just above the bedrock. If the bed-rock is badly broken or decomposed, the gold will be found in the cracks and crevices, and it will be found necessary to dig down  onto the bed-rock to make a good recovery of the gold values.

Gulch Placers - This type of placer is similar to the creek placer, except that the stream is usually intermittent in its flow or has been dried up altogether.

River-bar Placers - When bars of gold-bearing sand ,or gravel have been formed along the sides and in the center of the larger streams and rivers they are known as river-bar placers. The gold is often distributed throughout the bar and is generally fine as compared to the coarser gold found in the creek placers. Bar placers are generally low grade, but occasionally very rich bars are found.

Bench Placers.- Gravel-deposits of gold-bearing material in old (ancient) stream-channels and flood-plains which stand 50 to several hundred feet above the present stream or river level are called bench placers and represent the remnants of stream-beds which existed in the earlier stages of the stream-development.

Lake-bed Placers - Placers formed in the beds of present or ancient lakes formed by landslides or glacial dams across the gold-concentrating stream.

Sea-bed Placers - Placers re-concentrated from the sea-coast gravels by the action of the waves along the sea-shore.


MINERALS ASSOCIATED WITH PLACER GOLD

Placer gold nearly always occurs in association with “black sands,” the black sands being composed principally of grains of magnetite (magnetic iron oxide) and varying amounts of hematite (non-magnetic iron oxide), ilmenite (titanium iron oxide, and pyrite (iron sulphide), The specific gravity or density of placer gold is fifteen to nineteen times that of water, varying somewhat owing to different percentages of silver usually found alloyed with it. Magnetite has a density of five, so that placer gold is three to four times as heavy as magnetite, the chief constituent of the black sands. Quartz, the commonest rock found in association with gold, is only one-sixth to one-seventh as heavy as gold, and during the transportation and sorting of the placer-forming material, the quartz grains and grains of other light minerals and rocks are carried away while the gold, black sand, and other heavy minerals are dropped and, due to their weight and the sorting action of the stream, sift down between the boulders and pebbles until they come to rest on the bed-rock. Likewise in panning or in other methods of artificial separation of the gold from the placer-gravels. The black-sands and heavy minerals will remain longest with the gold and will be the last to be separated therefrom.

With a little experience and practice, gold is readily distinguished from other minerals, the ones which are usually the most deceiving being iron pyrite (fools gold) and bronze or golden-colored mica. Pyrite is brittle and is readily broken by crushing, whereas gold is malleable, and when it is hammered it simply flattens out into thin flakes without breaking. Mica is easily distinguished from gold by its light weight and the fact that when it is hammered it breaks into white-colored flakes.


SIZE OF GOLD) PARTICLES IN PLACERS

Placer gold is of all sizes, from large nuggets weighing several ounces (occasionally pounds) to minute specks known as “colors.” It usually occurs in flattened and rounded grains, and when it is found as angular and occasionally crystallized particles, nearness to the primary source of the gold is indicated. Gold retained on a 10-mesh screen (openings 1/15 inch square, approximately) is called course gold. Medium-sized gold varies from 1/15 to 1/30 inch in diameter, while fine gold from 1/30 down to 1/70 inch in diameter will average about 2,200 colors. Very  fine gold will average about 40,000 colors to the ounce, while flour-gold, or colors, readily visible in gold panning, will be so small that it will take over 1,000,000 of them to make an ounce of gold.


PROSPECTING FOR PLACER GOLD

Since Streams and their tributaries are the principal agencies in the formation of placer deposits, the first search for placer gold is generally made along the stream-beds, on the stream-bars, and the tributary gulches in areas that are known to be favourable for placer deposits.  Even though the valuable deposits of placer-ground may be located up on the benches of the stream, the presence of gold will almost invariably be indicated by showings obtained in test-panning done along the stream below.

In prospecting along a stream the prospector should pan the gravel at many points, selecting particularly such places as shows evidence of concentration of the minerals by the presence of black sands. Also, since the gold and heavy mineral will ordinarily be found concentrated on bed-rock, the placer prospector should carefully investigate all exposures of bed-rock along and in the stream, especially those impressions wherein minerals might easily be caught. Test pits to bed-rock on the bars and banks of the stream are also recommended in examining any areas which respond to preliminary stream-panning.  The results of panning tests are noted, preferably on a rough map or sketch prepared by the prospector, and if a section shows a better concentration in one or two points, the prospector should give some attention to the sinking of test-pits and prospecting the slopes above the stream-bank in an effort to find the best areas. 

The gold-pan is an indispensable tool in prospecting in either a large or small way.  It is a circular dish, nowadays, commonly made of plastic, with sloping sides, most of which comprise a series of riffles  which assists in trapping the gold and the heavier minerals, and varies in size from 7 to 18 inches in diameter, with a depth of 2½  to 3 inches. Gold-pans for the modern prospector, come in a variety of colors, with deep green, black and blue being the more favored by most. The pan should be light, but stiff enough to withstand hard usage, and be kept free from grease or oils.  Gold-pans of the ordinary type can be purchased from about seven dollars upward, at hardware stores, sporting supply outlets and prospecting supply dealers. The specialty pans may be purchased from local prospecting supply shops or through the internet.

In panning, experienced placer-miners will pan about 100 pans in 10 hours, the exact number depending on the coarseness of the gold, the amount of clay and cemented gravels panned, and the skill of the individual panning. The ordinary gold-pan holds about 265 cubic inches of gravel on the average, or 176 pans of gravel will correspond approximately to 1 yard of gravel in place.


TESTING OF PLACER

In small scale work or hand-work, prospecting, testing, and actual mining, whether panning, rocking, or sluicing, are usually all done at the same time. That is to say, the deposit is prospected as it is being mined, and the work is shifted from place to place according to the disclosures made during the progress of the work.  The results of pan samples are used as a guide in working the small property.

For large deposits of low-grade gravels which can only be worked profitably by mechanical means involving large capital expenditures, a thorough preliminary prospecting and testing of the deposit is required.  This is done by means of test-pits and drill-holes, depending on the characteristics of the deposit.  After the average values, yardage and distribution of the gold have been determined with accuracy, the following things must be considered before planning the actual methods of gold recovery: the thickness of gravel; the depth of overburden; the topography of the country; the nature of the bed-rock; the conditions governing the disposal of the washed gravels; the water-supply available; the character of the gravels, whether cemented, bouldery, or otherwise; the methods available for excavating, transporting, washing, and recovery of gold; as well as the local transportation and climate conditions.  The three most important are the extent and value of the deposit, the presence of adequate supplies of water, and tailings-disposal room on a gravity grade.


PLACER-MINING METHODS

Placer-mining is conducted by both underground and open-cut mining methods, the underground placer-mining being called " drift-mining " and employed for the mining of buried placer deposits. The open-cut methods of placer-mining may best be classified according to the equipment used, as follows:
(1.) Hand methods: (a) Panning; (b) rocking; (c) long-toms; (d) sluicing, including ground-sluicing and booming.
(2.) Power methods in conjunction with sluicing: (e) Drag-scraping; (f) hydraulic mining: (g) power-shoveling; (h) gold-dredging.
(3.) Dry placer-mining.
Placer-mining in principle implies the excavation or digging of the gravel, the transportation of the gravel to the equipment which disintegrates and washes it, and the removal of the waste tailings, followed by the recovery of heavy minerals caught in the gold or mineral-catching riffles.

The power methods of placer-mining all employ sluicing of some form for the recovery of the gold, the chief distinction between the power and the hand methods coming in the method and equipment used for excavating and conveying the gravels to the sluices.  The sluices are the same in principle in each case.
Only brief reference will be made herein, to the various methods of power working.

Hand methods of working are useful for small-scale operations on deposits of fairly high-grade gravel which are of shallow depth and covered with not more than a very shallow covering of barren material.

PANNING - The limitations of panning as regards the amount and grade of the material which can be profitably handled have already been indicated under notes above.  It is slow, laborious, back-breaking work which requires plenty of perseverance , but since the only tools used are a pick, shovel, and pan, it is often the favorite method for those not wishing to make a larger investment in equipment.

ROCKING – Rocking requires very little more in the way of equipment than panning, and it may be employed by the small operator to substantially increase the amount of gravel which he can wash in a day.  The rocker may be operated by one man, but two men are better, as one of them can be excavating and carrying the gravel while the other operates the rocker, turn and turn about.  Two men working steadily will was from 3 to 5 cubic yards of gravel per ten-hour day, the actual amount washed depending on the nature of the gravel, the distance it hast to be carried, etc.  The rocker is not greatly efficient, but the prospector can handle several times as much gravel in a day with it as by panning, and it can be used in areas where water is not plentiful, by carefully conserving the water in pits dug for the purpose (which could be lined with a plastic sheet, such as a tarpaulin ), the same water being used over and over again.

LONG-TOMS – The tom, or long-tom, is sometimes used in place of the rocker, but where running water and suitable grades prevail, the use of a simple sluice is just as effective and requires less labor.

SLUICING – There are many variations of sluices, of which the individual should explore for the more optimum designs, keeping in mind such unit should adapt to the operators intended application, but such depends for its success upon a plentiful supply of water, and sluicing is most easily conducted where the bed-rock has a good natural slope of at least 4 to five percent grade or more.  Where a favorable grade is not available it becomes necessary to adopt some mechanical means of handling the gravels in order to operate at all efficiency.  The gravel to be washed is generally introduced to the sluice through a head-box equipped with a grizzly (bar screen) made of poles or iron bars and pipe.  The spacing of the grizzly-bars will depend on the size of the gravel, and where fine gravel is to be washed, it is preferable to use a perforated screen, or even do without the grizzly, picking out the large boulders by hand as they become encountered.  Again, the equipment design and methods employed varies greatly amongst placer miners, and seldom is it seen that the individual does not modify his/her equipment to their own personal satisfaction.  Many making their sluice and associated hardware themselves.  Placer miners, however, are generally a tight-knit group and most are quite willing to share their designs, alterations and adaptations, for assisting others miners of less advantage.

OTHER PLACER MINING METHODS

Only brief mention will be made here, of other power-methods of placer mining, which have been employed for low-grade deposits with considerable overburden. With the exception of some countries around the globe where strict regulations regarding environmental issues have not yet been implemented, the  processes noted in following, are now either heavily regulated or in the most part, otherwise prohibited.  These being:
- Drag-Scrapers;
- Hydraulic-Mining;
- Power-Shoveling; and
- Dredging.
   Dredging, however, can be broken down to identify to large scale and small scale operations, the latter of which incorporates smaller equipment such as 2 to 6 inch dredges used more for recreational or advanced-level small-scale operations in some countries, including the US. Large scale dredging for gold recovery purposes in Canada, and in particular, British Columbia, is now a process of historical mention, and until most recently where permitting ”may” be in consideration but only under stringent stipulations, recreational dredging, per se, has been banned.

One further method previously used around the globe, which from an environmental and health perspective, and though effective, has proven a nightmare – this being the use of Mercury.

***SPECIAL NOTE***

The author hereto, GPEX, the Canadian Prospector’s Forum, its management and members, and, all environmental and health conscious miners, recreational enthusiasts and other individuals of the general public, in no way encourage nor condone the use of Mercury for any mining process, or other purpose, whatsoever. The dangers are well documented and supportive of the banning, thereof.  Please show your support and abide by your conscience – the individual's longevity of health and life you may save, may be either your own or that of a loved one, including your children and that of their offspring.  Thank you!
Somebody said that it couldn't be done
But he with a chuckle replied
That maybe it couldn't but he wouldn't be one
Who'd say so until he had tried.

Offline Auminer

  • Placer Miner and Photographer
  • PPT Invited
  • *****
  • Posts: 27
  • Province/State: Haines, Alaska
  • Kudos: 0
  • Alaska
    • Photographer
Re: Placer Deposits
« Reply #1 on: January 28, 2008, 12:30:21 PM »
Phew...very nicely done! 

Do you have a "sticker" option in simple machines? 
This post deserves it!!!
Dave

Offline gnome

  • PPT Invited
  • *****
  • Posts: 55
  • Province/State: Penticton B.C
  • Kudos: 0
Re: Placer Deposits
« Reply #2 on: February 05, 2008, 01:01:52 PM »
 if one does not use mercury to remove very fine and flour gold from the black sands what are some good methods to retrieve the gold . i'm very happy to see this topic because a hour ago i just finished panning out my black sand and see there is still lots of verry small stuff left. Iwas just about to try mercury to recover it (with extream caustioi might add) thank goodness I decided to take a break and do some reading first. I have about a pint of mercury what do you suggest Ido with it.I'm not interested in hurting my self ,the envi. or anyone else .thank for the greattopic























Offline jonniebud

  • PPT Invited
  • *****
  • Posts: 83
  • Province/State: british columbia
  • Kudos: 1
Re: Placer Deposits
« Reply #3 on: February 05, 2008, 01:57:59 PM »
you can try a sniffer bottle or splurdge and buy a seperator mercury can do serious harm to you

Offline gnome

  • PPT Invited
  • *****
  • Posts: 55
  • Province/State: Penticton B.C
  • Kudos: 0
Re: Placer Deposits
« Reply #4 on: February 06, 2008, 10:28:04 AM »
 well i used my sniffer bottle with a table top magnafing glass with a light that is attached to it it works great but theres still lots there guess next step is a separater any suggestions on what wors good for very fine stuff thanks

Offline rockpup

  • PPT Invited
  • *****
  • Posts: 1139
  • Province/State: Lethbridge, Alberta.
  • Kudos: 7
  • Yar der be gold in dem pans!!
Re: Placer Deposits
« Reply #5 on: March 13, 2008, 07:30:34 AM »
I seen something intresting on a site about mercury. Prospectors Paradise - Recreational Gold Prospecting he has alot of information about chemical separtion ect. I would never use mercury, even if I had a fume hood and a proper retort. I think one wiff of that stuff and its stuck in your body for good (heavy metals do not like to come out of the body mercury,lead). It does work, but theres other ways of going about gold seperation.

Offline GPEX admin

  • Administrator
  • **********
  • Posts: 2070
  • Province/State: Hope, BC Canada
  • Country: ca
  • Kudos: 47
  • Larry
    • GPEX Gold And Platinum Explorations
Re: Placer Deposits
« Reply #6 on: March 14, 2008, 03:20:47 AM »
Hi Guys...

Good to see better judgment over-rule the easy gold/mercury factor.  I wish to offer all placer miners two things for consideration...

1st  I would suggest anyone wishing to process their fine cons, sport the price of the book published by "Click the Yellow Chick", a member of this Forum.  She has extensively researched all facets of this science and compiled comprehensive data on this subject.  And has developed one or more excellent processes for the recovery of precious metals from placer cons.... and much more.  Well worth your while!  Her book is not that expensive, but is ever as important to the placer miner as is his gold pan, sluice, trommel or whatever equipment used.  You may send her a personal mail from this site to inquire about its acquisition.  Of her several posts, she may be easiest found in the Steppegold Section.

2nd  Though not specifically mining related, it has to do with toxins in the human body, which should be construed to include dangerous levels of metals, such as mercury and other concerning elements.  For a few years now I have been preached to relentlessly by a fellow miner/lady acquaintance from the Golden area, to start using liquid Zeolite.  All for the sake of improving upon one's health.  For anybody wishing to do the research, there is no better filtration on earth than Zeolite, and in its processed, condensed state, liquid Zeolite removes the vast majority of toxins from your body, if not all.  Finally, today, I picked up a bottle and am about to embark on a regime religiously.  It is outright scary what our intake is from food products alone, not to mention anything else we may come across.  And us as miners, oft times and quite unbeknown, expose ourselves to PGEs and other toxic mineralization in doses too great for the body to normally handle.  Thus, it accumulates.  And it would only stand to reason, from inhalation alone, we would not even know when contracting something, which in the end, could shorten life or otherwise cause for irreversible damage to organs and weird illnesses.  Personally, I too would recommend that everyone, including your loved ones and family members, consider this very important body cleanser.

And No.... I do not own stock in a Zeolite factory, either.  lol

Hope these offerings are found to be of help to everyone.
Somebody said that it couldn't be done
But he with a chuckle replied
That maybe it couldn't but he wouldn't be one
Who'd say so until he had tried.

Offline gnome

  • PPT Invited
  • *****
  • Posts: 55
  • Province/State: Penticton B.C
  • Kudos: 0
Re: Placer Deposits
« Reply #7 on: March 25, 2008, 12:15:59 PM »
Hey thanks Rockpup for sending me to that link it was a wealth of information i think everyone should have a look great information on lots and lots of things .thanks again. ;)

Offline karmakraze

  • Member
  • **
  • Posts: 2
  • Kudos: 0
Re: Placer Deposits
« Reply #8 on: April 04, 2008, 10:29:59 AM »
 {cool^sign} Thanks for all the awesome info On placer deposits. Does anyone know the best place to go panning near Creston, B.C. that i could walk or hike to?

Offline joetherock

  • PPT Invited
  • *****
  • Posts: 61
  • Province/State: alberta
  • Kudos: 0
Re: Placer Deposits
« Reply #9 on: July 12, 2008, 12:48:14 AM »
hey larry or any one else i have a query  about the density of the common gravels in a placer deposit  is it  under 6.095 where mercury is 13.534 cause was researching and  a metal called gallium liquid at + 39 c could this maybe act as a separating agent instead of mercury ?