AA PROSPECTOR’SPROSPECTOR’S GUIDE GUIDE TOTO VMS DEPOSITS IN AND LABRADOR

contributed by J. Geoffrey Thurlow VMS CONSULTANTS INC. Matty Mitchell Prospectors Resource Room Information Circular Number 1

First Floor, Natural Resources Building Geological Survey of Newfoundland and Labrador 50 Elizabeth Avenue, PO Box 8700, A1B 4J6 St. John’s, Newfoundland, prospectors Telephone: 709-729-2120, 709-729-6193 e-mail: [email protected] resource room Website: http://www.nr.gov.nl.ca/mines&en/geosurvey/matty_mitchell/ A PROSPECTOR’S GUIDE TO VMS DEPOSITS IN NEWFOUNDLAND AND LABRADOR

sulphide disseminations and veining in altered What are VMS Deposits? volcanic host rocks. This zone can be very ir- regular in shape. The alteration zone associated with most VMS deposits forms a much larger target than the massive sulphide and is olcanogenic massive sulphide (VMS) therefore one of the most important features to deposits are one of the most common V identify when prospecting for VMS deposits. A families of mineral deposits on earth. They massive sulphide district contains a cluster of consist of irregularly-shaped, tabular bodies of VMS deposits associated with a single or nearly 100% sulphides within volcanic host multiple alteration systems. rocks. Pyrite is generally the most abundant sulphide, though many non-Newfoundland There are several different classes of VMS deposits contain significant pyrrhotite. The base deposits and each member of each family is metals zinc (from sphalerite) and copper (from different from the rest. Don’t worry if your chalcopyrite) are the two most important com- prospect doesn’t look exactly like Buchans! modities produced from most VMS deposits; lead (from galena) is common, but less impor- tant economically. Many ores have important gold and silver credits which have a positive impact on the economics. Is Newfoundland and Labrador a Significant Canada may have the world’s greatest endowment of VMS deposits with great VMS District? districts like Noranda, Matagami, Bathurst and Flin Flon, rich deposits like Eskay Creek and Buchans and giant deposits like Kidd Creek and n a worldwide scale, the Appalachians in Manitouwadge. Ogeneral, and Newfoundland in particular, are recognized as an important VMS belt. They A typical VMS system consists of two main contain two of the world’s great VMS “camps”, ore types, (1) massive sulphide and (2) stringer Bathurst and Buchans. Both of these districts or stockwork ore with its associated alteration contained clusters of economic deposits which system. The massive sulphide is a much smaller could form the cornerstone of almost any target than the alteration zone and tends to be company. There has been significant production aligned in conformity with the host volcanic from other VMS deposits in Newfoundland strata. The stringer/stockwork zone forms be- (Rambler, Tilt Cove, Whalesback, Little Bay, neath the massive sulphide and consists of Pilley’s Island, Gullbridge, to name a few) and

1 a host of subeconomic deposits are known. Prospectors should take heart in the fact that Are VMS Deposits brand new VMS deposits are found in New- foundland virtually every year. The Archean an Attractive greenstone belts in Labrador should contain Exploration Target? economic VMS deposits, but exploration to date has not been encouraging. From a technical standpoint, these belts should be he short answer is YES! They’re attractive fertile ground for prospectors. Tto the prospector because there are plenty of showings and new deposits are being found Apart from the mineral potential, all the time. They’re attractive to companies Newfoundland has a lot going for it which because the deposit type is well known and has prospectors should be quick to point out to their an attractive economic profile. The combination clients. Newfoundland’s road and power of base and precious metals keeps these systems, abundant fresh water, proximity to deposits in vogue through the wild market tidewater, political stability (though this could swings that tend to knock the wind out of other be argued), eager labour force and historic deposits (gold being a good recent example). association with resource industries are all positive factors in selling your VMS prospect.

What to Look for How do VMS in the Field? Deposits Form? Boulders: Look for boulders of massive sul- phide or of altered and mineralized rock. Find deposits are a natural product of out the ice directions in the area and trace them VMShydrothermal activity as-sociated back to source. with submarine (underwater) volcanic activity worldwide. Seawater circulates through active Gossan: Pyrite is usually the most abundant volcanic rocks and becomes heated and picks sulphide in VMS deposits. Look for the telltale, up small quantities of metals from the rocks. yellowish rusty “burn” (weathering) on pyritic The heated, “pregnant” seawater is spewed onto outcrops; learn to distinguish between this and the sea floor as underwater geysers termed the more ochre-coloured carbonate alteration. “black smokers” from which the sul-phide But be on the lookout – some of the richest minerals precipitate. As you are reading this, deposits, like Buchans, are pyrite-poor and high black smokers are creating new VMS deposits grade boulders from these are not gossanous. at thousands of sites throughout the world. Hammer everything!

Alteration: If the alteration system is the hay- stack, the orebody is the needle. Chloritization, sericitization and pyritization are common and important. Silicification in small doses is a very

2 good sign. Visit Noranda (or closer yet, Gull- a greater probability of world-class size. bridge) and get to know what “dalmatianite” looks like. Rock Types: Volcanic rocks somewhere in the What Does a Buyer vicinity of your showing are a must for VMS deposits. VMS deposits form in a submarine Want to See? environment, on or below the ocean floor. Clearly then, it is important that the volcanic rocks which you are prospecting were deposited Regional Geology: Are there other VMS in a submarine environment. Pillow lavas are a deposits or mines in your belt? Felsic vol- sure sign of submarine extrusion and any canics? Subvolcanic intrusions? volcanic belt containing both pillow lavas and felsic volcanics is a good bet for VMS deposits. Volcanic Rocks: Are a “dime a dozen” but some textures are important. After you’ve Sulphide Clasts: Carefully examine any out- shown him some mineralization, make sure you crops of breccia for clasts which may be altered also show any good exposures of volcanic and mineralized, or better yet, for massive rocks. A variety of volcanic rock types is more sulphide clasts. promising than mountains of boring pillow lavas. Evidence of Faults: We all have our faults and so do VMS deposits. Faults containing ground- Structural Complexity: It’s a simple fact that up mineralized material are a very good sign. VMS deposits occur in structurally complex settings. Specific Features: Every VMS district is different and in each there’s one or two rock Alteration: The stronger, the better. Chloriti- types of extraordinary importance. At Matagami zation, sericitization and silicification are the it’s the “Key Tuffite”; at Buchans it’s the best signs. Chloritized felsic volcanics are “Granite Conglomerate”. Get to know the im- better than chloritized mafics. Areas of K- portant rocks in your area on an intimate basis! feldspar, carbonate and epidote alteration will raise some geologist’s eyebrows.

Mineralization: Disseminations of pyrite or Who Would be Interested pyrrhotite in altered rock are the first step. Stringers (irregular veinlets, preferably with in a VMS Showing? alteration selvedges) of pyrite with base metal sulphide are better than those without. Barite is a common gangue mineral in some VMS lmost any small to mid-sized minerals deposits and is a good sign – learn to identify it. Acompany with a base metals focus will be glad to examine your VMS property. Very large Grade: The visitor is going to want to see that companies need very large deposits to sustain there’s some indication of ore grades on the them in the long run. Because there are only a property. Unfortunately, there are a large few “giant” VMS deposits in the world (for number of “barren” or low grade VMS deposits example Kidd Creek at Timmins), some of the in Newfoundland (for example, big ones at largest companies prefer to look for porphyry , Pilley’s Island and in the copper and other types of deposits which offer Tulks Belt). You’ll have a harder sell if all you

3 can show is pyrite. On the other hand, large tool used by geologists to help quantify alter- zones of massive barren pyrite characterize ation. VMS alteration is a complex topic but the significant parts of some of the world’s great simplified bottom line is that soda (Na2O) VMS deposits. In Newfoundland, the Duck depletion is an important characteristic of the

Pond deposit is dominantly massive pyrite but alteration zones at all VMS mines. Na2O contains an ore grade core. Due to the realities contents in volcanic rocks of less than 1% will of the market and smelting considerations, arouse interest and less than 0.1% will have deposits which contain higher proportions of some geologists turning cartwheels. Most copper and precious metals (gold and silver) geologists visiting your property will want to will be valued more highly than those which do take a sample or two; copies of their results will not. be of interest to the next visitors.

Previous Work: A new prospect will hold more mystery than a property that has been “killed” General Advice with hundreds of drill holes.

Value added features: Geochemical or geo- , Size is not everything at the prospecting physical anomalies will make your property stage. Your showing may only be small, more interesting. but many important VMS deposits do not even come to surface and are completely Geochemical Anomalies: Soil geochemistry is covered by “dead-looking” rocks (these are generally a very effective VMS exploration called “blind” deposits). Because most of technique in Newfoundland. If you can’t sell the obvious outcropping deposits have your prospect as it is, consider doing a small already been found, blind deposits, or those soil geochemical survey to demonstrate un- showing just a small area of altered rocks at tested potential. surface are where the next generation of VMS deposits will be found. Geophysical Anomalies: EM, IP, magnetic and gravity surveys are the most common geo- , Get out and visit as many VMS deposits, physical methods used in the search for VMS prospects and mines as you can. You’ll see deposits. Chalcopyrite and pyrrhotite are the lots of important things that can’t be two most conductive VMS minerals and crammed into a short write-up. deposits containing appreciable amounts of these are excellent EM conductors. On the other , Be assured that there really are plenty of hand, deposits with lots of sphalerite and barite undiscovered VMS deposits in Newfound- are may only be weak conductors. VMS de- land and Labrador. There’s one out there posits and their mineralized alteration zones waiting for you. Good luck! produce strong Induced Polarization anomalies. Some VMS deposits contain abundant magne- J. Geoffrey Thurlow tite and are strongly magnetic. Be aware that VMS Consultants Inc. strong EM, IP, magnetic and gravity responses March, 2000 can be produced (and indeed are most com- monly produced) by sources which are not of economic interest.

Lithogeochemistry: Whole rock geochemistry (or “lithogeochemistry”) has become a standard

4