Chapter 1 Prospecting and the Exploration Process This chapter attempts to put the detailed exploration procedures outlined in this book into the wider context of the whole exploration process from first concept to ore discovery. 1.1 Definition of Terms Exploration field activities take place as part of a strategy (often called a"play")to locate and define a particular economically mineable mineral commodity (ore)in a mineral province.Large exploration plays are often broken down into individual projects(often a particular tenement!group)and each project may contain one or more prospects is a restricted volume of ground that is considered to have the ing an ore body ands ally a nam ed geographical loc ne,an area sele on the basis of some geological idea,or perhaps some anomalous feature of the environment(usually a geophysical or geochemical measurement)that can be inter. preted as having a close spatial link with ore.Prospects are the basic units with which explorationists work.The explorationist's job is to generate new prospects and then to explore them in order to locate and define any ore body that might lie within them. 1.2 Generating New Projects and Prospects Generating new prospects is the critical first stage in the exploration process and is known as ecting.Traditionally,prospecting was the search for simple visual s of mineralization. owadays the range of surface indication plore and min differ non-specific way to refer to all such titles. R.Maroribanks.Geological Methods in Mineral Exploration and Mining.2nd ed. DOI 10.1007/978-3-540-74375-0_1.Springer-Verlag Berlin Heidelberg 2010
Chapter 1 Prospecting and the Exploration Process This chapter attempts to put the detailed exploration procedures outlined in this book into the wider context of the whole exploration process from first concept to ore discovery. 1.1 Definition of Terms Exploration field activities take place as part of a strategy (often called a “play”) to locate and define a particular economically mineable mineral commodity (ore) in a mineral province. Large exploration plays are often broken down into individual projects (often a particular tenement1 group) and each project may contain one or more prospects. A prospect is a restricted volume of ground that is considered to have the possibility of directly hosting an ore body and is usually a named geographical location. The prospect could be outcropping mineralization, an old mine, an area selected on the basis of some geological idea, or perhaps some anomalous feature of the environment (usually a geophysical or geochemical measurement) that can be interpreted as having a close spatial link with ore. Prospects are the basic units with which explorationists work. The explorationist’s job is to generate new prospects and then to explore them in order to locate and define any ore body that might lie within them. 1.2 Generating New Projects and Prospects Generating new prospects is the critical first stage in the exploration process and is known as prospecting. Traditionally, prospecting was the search for simple visual surface indications of mineralization. Nowadays the range of surface indications 1The legal title to explore and mine an area goes by different names in different countries and carries a wide variety of rights and obligations. The word “tenement” is used in this book in a non-specific way to refer to all such titles. R. Marjoribanks, Geological Methods in Mineral Exploration and Mining, 2nd ed., 1 DOI 10.1007/978-3-540-74375-0_1, C Springer-Verlag Berlin Heidelberg 2010
2 I Prospecting and the Exploration Process that can be recognized by the explorationist is expanded by the use of sophisticated geophysical and geochemical techniques.However.the skills and abilities involved in successful prospecting are common to all techniques.They involve activity observation,knowledge.insight,opportunism.persistence.lateral thinking and luck A description of traditional prospecting skills will therefore serve to illustrate these key attributes s of succes i places likeAustra a or North America.it wa still possibleto stumbl on a kilometr -long prominent ridg e of secondary lead nerals,or a district where ubiquitous green secondary copper mi indicated the huge porphyry system beneath.Even as late as the second half of the twentieth century,prominent and extensive mineralized outcrop were still being identified in the more remote parts of the world.Discoveries such as Red Dog in Alaska(Kelley and Jennings,2004:Koehler and Tikkanen,1991).Porgera in Papua New Guinea (Handley and Henry,1990)and Ertsberg in West Irian (Van Leeuwe 1994).belong to this era.Few olaces are left in the world today which offer such readily identid ation is increas ngly foc sed on the search for dies that have ither subtl ou crop or ne all. spite o exper ws that prospecting meth can still find ore bodies.Good examples of this are the 1964 discovery of the West Australia nickel sulphide deposits at Kambalda (Gresham,1991):the 1982 discovery of the massive Ladolam Gold Deposit of Lihir Island.Papua New Guinea (Moyle et al.1990).the 1993 discovery of the outcropping gossans which overlay the rich Voisey Bay Cu/Ni/Co massive sulphide ore body in Labrador.Canada (Kerr and Ryan.00)the discoverof he massive yu Tolgoi CuAu porphyry in of the l arge Sukari gold de po sit in the easterd gypt2(Helmy et al.2004 If re ineral discoveries are examined,it seems that success has come from three main factors: 1.The explorer searched where no one had searched before.This may be because historical or political opportunity made an area accessible that previously was inaccessible.However,very often the reason for the discovery was simply that no one had previously thought to look in that particular place. 2.The explorer identified and tested subtle or non-typical indications of mineral- ization that had previously been overlooked,either because they were very small or,more usually,because he recognized as significant some feature that previous re had sae riten (00) ntly 2Oyu Tolgoi and Sukari were both areas of minor known mineralisation and artisanal mining going back thousands of years.However,their true size was not suspected until modem exploration was
2 1 Prospecting and the Exploration Process that can be recognized by the explorationist is expanded by the use of sophisticated geophysical and geochemical techniques. However, the skills and abilities involved in successful prospecting are common to all techniques. They involve activity, observation, knowledge, insight, opportunism, persistence, lateral thinking and luck. A description of traditional prospecting skills will therefore serve to illustrate these key attributes of success. During the nineteenth century, in places like Australia or North America, it was still possible to stumble on a kilometres-long prominent ridge of secondary lead and zinc minerals, or a district where ubiquitous green secondary copper minerals indicated the huge porphyry system beneath. Even as late as the second half of the twentieth century, prominent and extensive mineralized outcrop were still being identified in the more remote parts of the world. Discoveries such as Red Dog in Alaska (Kelley and Jennings, 2004; Koehler and Tikkanen, 1991), Porgera in Papua New Guinea (Handley and Henry, 1990) and Ertsberg in West Irian (Van Leeuwen, 1994), belong to this era. Few places are left in the world today which offer such readily identified prizes. For that reason, exploration is increasingly focused on the search for ore bodies that have either subtle outcrop or no outcrop at all. In spite of this, experience shows that simple prospecting methods can still find ore bodies. Good examples of this are the 1964 discovery of the West Australia nickel sulphide deposits at Kambalda (Gresham, 1991); the 1982 discovery of the massive Ladolam Gold Deposit of Lihir Island, Papua New Guinea (Moyle et al., 1990), the 1993 discovery of the outcropping gossans which overlay the rich Voisey Bay Cu/Ni/Co massive sulphide ore body in Labrador, Canada (Kerr and Ryan, 2000), the discovery in 1996 of the massive Oyu Tolgoi Cu/Au porphyry in Mongolia (Perello et al., 2001) and the discovery of the large Sukari gold deposit in the eastern desert of Egypt2 (Helmy et al., 2004). If recent mineral discoveries are examined, it seems that success has come from three main factors: 1. The explorer searched where no one had searched before. This may be because historical or political opportunity made an area accessible that previously was inaccessible. However, very often the reason for the discovery was simply that no one had previously thought to look in that particular place. 2. The explorer identified and tested subtle or non-typical indications of mineralization that had previously been overlooked, either because they were very small or, more usually, because he recognized as significant some feature that previous observers had seen but dismissed as unimportant. As Dick Sillitoe3 has recently written (Sillitoe, 2004): 2Oyu Tolgoi and Sukari were both areas of minor known mineralisation and artisanal mining going back thousands of years. However, their true size was not suspected until modern exploration was undertaken. 3Richard Sillitoe is a well known international economic geology consultant
1.3 Some Ways of Generating New Exploration Ideas 3 Careful scrutiny of bedrock outcrops.some perhaps only meters across.is a key part of successful exploration- -because it may reveal the subtle distal signatures of concealed Recent experience shows.however,that such detaile raversing,even o its which have simpl 3.In areas of known mineralisation ("brownfield"exploration),the explorer employed step-out holes to locate non-outcropping ("blind")mineralisation below cover.This type of exploration can only be successful where geological knowledge gained from the established mines and prospects gives the explorer confidence to embark on extensive(and expensive)drilling programs in areas that lack outstanding surface indications.Examples of successes from this type of exploration are the discovery by Newcrest at Cadia,NSW,Australia of th eposit belw rlying sediment(Holida One of the most important ingredients of prospecting success has been lateral thinking.By this is meant the ability to: see familiar rocks in new contexts pecially one's own)and accepted wisdom uch (since some of the aboveributr mch subconscious as conscious). 1.3 Some Ways of Generating New Exploration Ideas New ideas may come"out of the blue",but more often are the result of certa well-recognized situations that the explorationist is able to combine fruitfully with knowledge that they already have.It pays him to be alert for these situations so as to take advantage of the opportunities that they offer.Here are some of them: 1。 Merlin)in the mt isa inlier ou totoudrlnuanofurd Premnar papr on Mern by Forno Lazo and amal Lal can be found at ww.smedg.org-au (Access physicist Richard Feynma n said:"The first principle is that you 6 place in the der left side.Both p lay a part in successful ore finding
1.3 Some Ways of Generating New Exploration Ideas 3 Careful scrutiny of bedrock outcrops, some perhaps only meters across, is a key part of successful exploration—because it may reveal the subtle distal signatures of concealed mineralisation. Recent experience shows, however, that such detailed traversing, even of the most highly explored terranes, by experienced practitioners can also pinpoint partly outcropping deposits which have simply gone undiscovered because the subtle surface expressions are both invisible from the air and on satellite imagery. The oft quoted notion that all wholly or partly exposed deposits have been found in the world’s mature belts is, to my mind, a myth. 3. In areas of known mineralisation (“brownfield” exploration), the explorer employed step-out holes to locate non-outcropping (“blind”) mineralisation below cover. This type of exploration can only be successful where geological knowledge gained from the established mines and prospects gives the explorer confidence to embark on extensive (and expensive) drilling programs in areas that lack outstanding surface indications. Examples of successes from this type of exploration are the discovery by Newcrest at Cadia, NSW, Australia of the Ridgeway porphyry Cu/Au deposit below 450 m of overlying sediment (Holiday et al., 1999) and the 2009 discovery of Merlin Cu/Mo/Au prospect by Ivanhoe Australia Ltd.4 One of the most important ingredients of prospecting success has been lateral thinking. By this is meant the ability to: • see familiar rocks in new contexts • question all assumptions (but especially one’s own5) and accepted wisdom • be alert for small anomalies or aberrations • know when to follow a hunch6 (since some of the above attributes are as much subconscious as conscious). 1.3 Some Ways of Generating New Exploration Ideas New ideas may come “out of the blue”, but more often are the result of certain well-recognized situations that the explorationist is able to combine fruitfully with knowledge that they already have. It pays him to be alert for these situations so as to take advantage of the opportunities that they offer. Here are some of them: 4In 2009, Ivanhoe Australia announced discovery of a significant new Mo/Rh/Cu deposit (called Merlin) in the Mt Isa Inlier, Queensland, Australia. The discovery was the result of persistence and a commitment to step-out drilling around known mineralisation in one of Australia’s most explored Cu/Au provinces. A preliminary paper on Merlin by Florinio Lazo and Tamal Lal can be found at www.smedg.org.au (Accessed Dec 2009). 5As the famous twentieth century physicist Richard Feynman said: “The first principle is that you must not fool yourself – and you are the easiest person to fool.” 6A current theory is that intuitive and often subconscious processes take place in the right side of the brain, while rational, deductive reasoning derives from the left side. Both processes play a part in successful ore finding
1 Prospecting and the Exploration Process Scenario I:New knowledge of the geology or geophysics of an area becomes available from new mapping (either your own or Geological Survey maps). Combined with your own understanding of mineralization,the new mapping indicates the possibility of different styles of mineralization being pres ent o different places to look. :Elsewhere inadistrict that you are exploringa discovery is made which can be used as a new and more relevant model for mineralization than the one that you have been using. Scenario 3:A visit to other mining camps,maybe even on the other side of the world,provides new insight into your exploration property.The formal description of an ore body in the literature is no substitute for seeing it for yourself-particularly if there is an opportunity to see the discovery outcrop Scenario 4:Newly developed exploration technologies and/or methodologies lore effectively in an area where earlier r prospecting Scenario5:Political changes make available for exploration and mining a part of the world that previously had not been subject to modem methods of exploration. 1.4 A Check-List of Negative Assumptions Sooner or later in most exploration programmes on an area,an impasse is reached in the ability to generate new exploration ideas.At this point,it is always easy to think of many good reasons why the effort should be abandoned.However,before this decision is made,it is worthwhile to critically check through a list of the beliefs that are held about the area.On examination,these beliefs might turn out to be mere ptions,and the ght he .To assist in this negative assumptions commonly made by explorationists abou The area is not prospective because it is underlain by rock type X. Comment:How do you know?The geological map you are using might be wrong or insufficiently detailed.In any case,if rock type X is not prospective for your target commodity.perhaps it is prospective for some other commodity. .The area has already been exhaustively explored Comment:An area or prospect can almost never be exhaustively tested.Earlier explorers gave up because they ran out of ideas,time or money.The best any explo rationist can ever hope to do is to exhaustively test some idea or model that t ey hav about mineralizatio using the best their disposal at that time.Ger new model,simply find capital,and th area may turn out to be under-explored
4 1 Prospecting and the Exploration Process Scenario 1: New knowledge of the geology or geophysics of an area becomes available from new mapping (either your own or Geological Survey maps). Combined with your own understanding of mineralization, the new mapping indicates the possibility of different styles of mineralization being present or different places to look. Scenario 2: Elsewhere in a district that you are exploring, a discovery is made which can be used as a new and more relevant model for mineralization than the one that you have been using. Scenario 3: A visit to other mining camps, maybe even on the other side of the world, provides new insight into your exploration property. The formal description of an ore body in the literature is no substitute for seeing it for yourself – particularly if there is an opportunity to see the discovery outcrop. Scenario 4: Newly developed exploration technologies and/or methodologies make it possible to explore effectively in an area where earlier prospecting methods were unsuccessful. Scenario 5: Political changes make available for exploration and mining a part of the world that previously had not been subject to modern methods of exploration. 1.4 A Check-List of Negative Assumptions Sooner or later in most exploration programmes on an area, an impasse is reached in the ability to generate new exploration ideas. At this point, it is always easy to think of many good reasons why the effort should be abandoned. However, before this decision is made, it is worthwhile to critically check through a list of the beliefs that are held about the area. On examination, these beliefs might turn out to be mere assumptions, and the assumptions might be wrong. To assist in this process, here is a check-list of five negative assumptions commonly made by explorationists about the prospectivity of an area. • The area is not prospective because it is underlain by rock type X. Comment: How do you know? The geological map you are using might be wrong or insufficiently detailed. In any case, if rock type X is not prospective for your target commodity, perhaps it is prospective for some other commodity. • The area has already been exhaustively explored. Comment: An area or prospect can almost never be exhaustively tested. Earlier explorers gave up because they ran out of ideas, time or money. The best any explorationist can ever hope to do is to exhaustively test some idea or model that they have about mineralization using the best tools at their disposal at that time. Generate a new model, develop a new tool or simply find new access to risk capital, and the area may turn out to be under-explored
1.5 Stages in Prospect Exploration 5 .All prospective rocks in the area are pegged (staked)by competitors. Comment:When was the last check made on the existing tenements plan?Have all the opportunities for joint venture or acquisition been explored?If you have ideas about the ground which the existing tenement holder does not,then you are in a very good position to negotiate a favourable entry. .No existing ore-body model fits the area Commnent:Mineral deposits may belong to broad classes.but each one is unique detailed models are usually formulated after an ore body is found.Beware of looking too closely for the last ore body,rather than the next. .The prospective belt is excluded from exploration by reason of competing land use claims (environmental.native title.etc.). one is to ughe in the regulatory climate of many countrie ces are very high that beli efs in this a rea are not mere assumptions ith reason common sense and preparedness to compromise,patience and negotiation can often achieve much. 1.5 Stages in Prospect Exploration Once a prospect has been identified,and the right to explore it acquired,assessing it involves advancing through a progressive series of definable exploration stages. Positive results in any stage will lead to advance to the next stage and an escalation of the exploration effort.Negative results mean that the prospect will be discarded, sold or joint ventured to another party,or simply put on hold until the acquisition of fresh inf mation/ideas/technology leads to its being reactivated. be some gh the grea mean that there will diffe in ssible prospec type xplora on proces dividual cases,prospect exploration will generally go through the stages listed below. 1.5.1 Target Generation This includes all exploration on the prospect undertaken prior to the drilling of hole directly targeted on potential ore.The aim of the exploration is to detine such targets The procedures carried out in this stage could include some or all of the following: toanyone (you could afer all be wrong)
1.5 Stages in Prospect Exploration 5 • All prospective rocks in the area are pegged (staked) by competitors. Comment: When was the last check made on the existing tenements plan? Have all the opportunities for joint venture or acquisition been explored? If you have ideas about the ground which the existing tenement holder does not, then you are in a very good position to negotiate a favourable entry.7 • No existing ore-body model fits the area. Comment: Mineral deposits may belong to broad classes, but each one is unique: detailed models are usually formulated after an ore body is found. Beware of looking too closely for the last ore body, rather than the next. • The prospective belt is excluded from exploration by reason of competing land use claims (environmental, native title, etc.). Comment: This one is tougher; in the regulatory climate of many countries today, the chances are very high that beliefs in this area are not mere assumptions. However, with reason, common sense and preparedness to compromise, patience and negotiation can often achieve much. 1.5 Stages in Prospect Exploration Once a prospect has been identified, and the right to explore it acquired, assessing it involves advancing through a progressive series of definable exploration stages. Positive results in any stage will lead to advance to the next stage and an escalation of the exploration effort. Negative results mean that the prospect will be discarded, sold or joint ventured to another party, or simply put on hold until the acquisition of fresh information/ideas/technology leads to its being reactivated. Although the great variety of possible prospect types mean that there will be some differences in the exploration process for individual cases, prospect exploration will generally go through the stages listed below. 1.5.1 Target Generation This includes all exploration on the prospect undertaken prior to the drilling of holes directly targeted on potential ore. The aim of the exploration is to define such targets. The procedures carried out in this stage could include some or all of the following: 7It is usually a legal (and also a moral) requirement that all relevant factual data be made available to all parties in any negotiation on an area. Ideas, however, are your intellectual property, and do not have to be communicated to anyone (you could after all be wrong)