Latitude: 48° 13' 18" N
Longitude: 84° 18' 32" W
NTS: 42C01
Swanson Lake, site of the Bird reverse magnetic anomaly, is located in the southeastern corner of Bird Township 43 km northeast of the Municipality of Wawa in Northern Ontario (Figure 1). Bird Township is accessible year round from Wawa by a combination of highways and a series of well established lumber roads.
Property
Chalice Diamond holds a 100% interest in the Bird property, which is part of an option deal that includes a much larger land package in the area.
The Bird property consists of Bird Township and a group of nine claims staked by Chalice Diamond in neighbouring Bruyere Township to the east, which act as a buffer on the east side of a geophysical target, the Bird Anomaly (Figure 2).
Geology
Bird Township and the surrounding region is underlain predominantly by supracrustal rocks of Archean age (older than 2.5 billion years) composed of metavolcanic and metasedimentary rocks with various mafic and felsic intrusions. In southern Bird Township a prominent metasedimentary sequence consisting of thin units of chert magnetite iron formation with minor sulphides occurs between intermediate to mafic flows.
Numerous intermediate to mafic intrusions are present within the metavolcanics. These intrusive units vary in composition from quartz diorite to gabbro. Quartz-feldspar porphyry intrusions straddle the western boundary of Bird Township. The supracrustal and enclosed intrusions are cut by a northwest trending set of diabase dykes, which commonly occupy shear zones or faults.
The supracrustal rocks have been folded into a large regional anticline which has been cut by northwest to north trending faults. Along Manitowik Lake a major regional northeast trending fault is present. This fault is one of several faults related to the Kapuskasing Structural Zone (Figure 1), a zone where rocks formed in the lower continental crust are exposed at surface. The supracrustal rocks and enclosed intrusions are metamorphosed to the greenschist facies.
In the southeastern part of the township a large reverse magnetic anomaly is present that is similar to one that hosts the Eagle nickel-copper-PGE magmatic sulphide deposit that is in the permitting stage by Kennecott Minerals in Northern Michigan. (See below)
Previous Exploration Work
Fifteen mineral occurrences are listed for Bird Township in the Mineral Deposit Inventory, representing the results of gold and base metal prospecting and exploration from the 1920s through the 1990s.
The previous exploration work in the township was predominantly for gold and base metals. In the vicinity of Swanson Lake where the reverse magnetic anomaly is centred Leitch Gold mines came across some low gold values in the area of a magnetic anomaly in the early 1940s.
In 1972, the Resident Geologist from the Sault Ste. Marie office investigated the "negative magnetic anomaly" (Bird Anomaly) around Swanson Lake and confirmed the presence of a sequence of very magnetic basic flows and tuffs.
Work by Chalice Diamond
A helicopter-borne total magnetic intensity and time domain electromagnetic (VTEM) survey was carried out over the easternmost 81 sq km of the property in 2006 (Figure 3). This survey is referred to as 'Bird I'. A second VTEM survey known as Bird II was subsequently flown and focused on the Bird Anomaly (Figure 4).
Results of the Bird II survey suggest the Bird Anomaly consists of three separate high intensity magnetic nodes: a 'western', a 'lake' and an 'eastern' node.
An orientation survey for both conventional soil and Mobile Metal Ion (MMI) sampling was conducted along the length of the Bird Anomaly and with two lines across the anomaly (Figure 5). Top response ratios were calculated for the MMI orientation survey. (A MMI response ratio is simply a ratio between the background value of a particular element, say nickel, and the values for that element obtained from the survey. The higher the ratio the better the chance that that particular element is present in abundance at depth.)
When superimposing top MMI response ratio anomalies of metallic affinity on a trace of the three magnetic nodes, copper and nickel anomalies correlate with all three nodes.
Additionally, the top gold anomaly and its pathfinder metal bismuth, as well as the trace elements cadmium (an indicator for copper, lead and zinc) and cobalt (an indicator for nickel and copper) all coincide with the eastern node.
Subsequently, an extensive MMI survey has been completed over the Bird Anomaly. The results of the most recent MMI survey are pending.
The Bird Anomaly
The Bird reverse magnetic anomaly has been an enigma, but recent work initiated on behalf of the company has made progress into its understanding. For instance the Bird Anomaly coincides with or closely parallels the regional northeast-trending Wawa-Hawk-Manitowik Fault (WHMF), which is part of the Kapuskasing Structural Zone (Figure 1). The western node of the Bird Anomaly is developed where a north-northwest-trending semi-regional fault intersects the WHMF. The cause of the magnetic anomaly is not apparent at surface. The peridotites on surface are positively magnetic even though they are within a very large reverse magnetic terrain.
Within the confines of the Bird Anomaly the cause of the magnetic anomaly is not apparent in outcrop at surface. Therefore it is considered to be related to a buried intrusive beneath the rocks exposed at surface. Some surface expression of the intrusive may occur under various swamps in the area.
Proposed Work and Schedule
The target for the Bird property is a nickel-copper-platinum group element (PGE) magmatic sulphide deposit similar to the type found at Kennecott's Eagle deposit in Northern Michigan.
Work carried out to date has shown that there are similarities to the Eagle deposit such as host rock, method of emplacement and possibly age. To advance the project to the next stage, the VTEM and MMI results will be compiled and reviewed to generate drill hole locations for testing nickel-copper-PGE mineralization.
Peridotite intersected in drilling will be tested to determine whether the rock is depleted in sulphur. This will help guide future drill hole placement. Downhole geophysics will also be used to determine the proximity of conductive material in the vicinity of the drill hole itself.
Drill core will also be studied under the microscope to determine the nickel content of the olivine minerals that make up the peridotite rock. This approach will help determine whether nickel in the original magma would have been scavenged by sulphur or if insufficient sulphur was present, the nickel would end up in the lattice of olivine minerals, essentially eliminating them from forming nickel sulphide minerals.
In the model for mineralization that is contemplated for the Bird Anomaly, it is thought that a magmatic sulphide chamber may have formed, but has not been exposed at surface in outcrop. The chamber, which is conjectured to be the cause of the reverse magnetic anomaly, could be covered by a very thin veneer of magnetically positive rocks or it could be covered by swamp or overburden. There is a large swamp coinciding with the strongest magnetic response to the southwest of Swanson Lake.
Diamond Chalice's geophysicist will study the results of the VTEM surveys and look for the highest magnetic intensity after eliminating the effects of the overlying positive magnetic rocks. By determining the location of the highest reverse magnetic intensity, a drill plan can be made that maximizes the chances of intersecting significant sulphide mineralization.
The source of sulphur needed to concentrate the nickel, copper, and PGEs could be the iron formation that is located in the southeast corner of Bird Township.
The first geophysical survey (Bird I) outlined a fold-like structure in the southeast of the township, that is highly magnetic due to the presence of an iron formation. The nose of the fold should be where the reverse magnetic anomaly is located, but if there has been a magma intrusion here it would have eliminated the nose and the sulphide in the iron formation could have acted as the source of sulphur needed to concentrate the metals in the magma thus creating a sulphide deposit.
According to the United States Geological Survey, by having the appropriate geology, age of rocks and a sulphur source, the chances of finding a nickel deposit on the scale of Noril'sk or Voisey's Bay, is greatly enhanced. These three conditions are present at the Bird Anomaly. The anomaly with its three nodes of high magnetism measures over 6 km long and over 1.5 km wide. The size of the anomaly is unusually large, increasing the chances that mineralization in economic quantities could be present.
Other targets in the vicinity of Swanson Lake include gold and diamonds.
North of Cawdron Lake the VTEM survey outlined a linear feature that is a kimberlite dyke. It is oriented east-west and measures one to two kilometres long. About two kilometres to the west and directly on strike with this linear feature is a round lake just to the northwest of the western end of Cawdron Lake. The geophysical expression and the round shape of the lake make it an ideal target to test for the presence of a kimberlite pipe.
A second east-west linear magnetic feature has been outlined by the VTEM surveys, between Swanson Lake and Cawdron Lake. This geophysical feature requires ground investigation to determine its potential as a kimberlite dyke.
The presence of small high-grade gold mineralization that was found in the past may in part be explained by the remobilization and concentration of gold by the intrusion of kimberlite dykes in the area. Using this as a model for gold emplacement, these gold showings are exploration targets.
The presence of the Bird reverse magnetic anomaly has been known for a long time, but only recently has its significance as a nickel-copper-PGE magmatic sulphide exploration target been realized. The discovery of the Eagle deposit in nearby Michigan resulted in the creation of a similar deposit model for the Bird Anomaly. The reverse magnetism, the presence of similar rocks as at the Eagle deposit, the large size of the Bird Anomaly, the intensity of the magnetism and the overlapping of high MMI response ratios with the strongest magnetic responses point to an excellent exploration target for the presence of a nickel-copper-PGE magmatic sulphide deposit.
Eagle Deposit
On the south side of Lake Superior on the Upper Peninsula of Michigan, Kennecott Exploration discovered the high-grade Eagle nickel-copper-PGE magmatic sulphide deposit that is now at the permitting stage.
The geologic resource estimate for the deposit is 4.05 million tonnes with an average grade of 3.57% Ni, 2.91% Cu, 0.10% Co, 0.28 g/t Au, 0.73 g/t Pt and 0.47 g/t Pd.
The deposit is located near the mid-continent rift, a large scale failed continental rift that extends northeast from Kansas, passes beneath Lake Superior, and turns southward into southern Michigan (Figure 6).
The rift was formed when the continental plate was being pulled or forced apart sometime between 0.9 to 1.6 billion years ago. It is believed to be related to a mantle plume and is characterized by large-scale volcanism. The Eagle intrusion is hosted in a distinct intrusive rock (peridotite) that is part of an intrusive event ascribed to an early phase of rift-related volcanism.
A distinguishing geophysical feature associated with the peridotite that hosts the Eagle deposit is reverse polarity of the magnetic minerals. When the magnetic minerals in the peridotite were formed they were oriented to reflect the orientation of the Earth's north and south magnetic poles at the time, which is opposite to the present day configuration.
How Nickel-Copper Sulphide Deposits Are Formed
The basic requirements for the formation of nickel-copper sulphide deposits requires certain conditions and a specific sequence of events.
The formation of these deposits starts with the melting of hot mantle rising as a plume from deep within the Earth.
The melting produces basaltic magma that is relatively rich in metals but poor in sulphur, which then rises upward, intrudes into the crust, forming magma chambers. In these chambers, basaltic magma may interact and become contaminated by the crust. Sulphur from the surrounding rocks may be incorporated into the magma. This contamination reduces the ability of the magma to keep sulphur in solution, and the magma may become sulphur saturated. When sulphur saturation occurs, droplets of sulphide liquid form; because the droplets are more dense than basaltic magma, they tend to settle into the lower part of the magma chamber.
As the sulphide droplets segregate, they scavenge metals such as nickel, copper, platinum and palladium from the magma. If these sulphide droplets become sufficiently concentrated, a magmatic sulphide deposit is formed. The largest concentrations of sulphides appear to form in channels or conduits through which new magma flows into the magma chamber. Basaltic lavas erupted from chambers undergoing sulphide segregation will be depleted in those elements enriched in the sulphide deposits. Recognition of such depleted basalts can therefore provide important evidence that sulphide separation has occurred at depth.
