For those that are interested in reading...

can be found at http://gsc.nrcan.gc.ca/mindep/synth_...

Would be nice to some day see Beardmore-Geraldton Camp included in the same sentences as Timmins and Red Lake in recognition of scale...

Key features of these Canadian districts are: 1) presence of ultramafic-mafic volcanic rocks (including variolitic basalts); 2) major compressional crustal-scale faults; 3) presence of competent intrusions; 4) district-wide zones of carbonate alteration; and 5) presence of a regional Timiskaming-like unconformity. Other important features include: I) curves, bends and dilational jogs in the major crustal-scale fault; II) metamorphism not higher than amphibolite grade; III) size of the greenstone belt (smaller belts lost in intrusive and highly metamorphosed rocks, are yet to be proven as productive as larger ones); and IV) well-developed set of subsidiary faults and shears near the major crustal-scale fault.

Geological Properties

Continental scale

Greenstone-hosted quartz-carbonate-vein deposits typically occur in deformed greenstone belts of all ages, especially those with commonly variolitic tholeiitic basalts (Figure 12A) and ultramafic komatiitic flows intruded by intermediate to felsic porphyry intrusions, and sometimes with swarms of albitite or lamprophyre dykes (e.g. Timmins and Red Lake districts) (Figure 12B). These deposits are associated with collisional or accretionary orogenic events (cf. Kerrich et al., 2000 and references therein). They are typically distributed along reverse-oblique crustal-scale major fault zones, commonly marking the convergent margins between major lithological boundaries such as volcano-plutonic and sedimentary domains (e.g. Cadillac-Larder Lake fault) (Figure 3, Figure 12C, D). These major structures are characterized by several increments of strain, and consequently multiple generations of steeply dipping foliations and folds resulting in a fairly complex geological collisional setting. The crustal-scale faults are thought to represent the main hydrothermal pathways towards higher crustal levels. However, the deposits are spatially and genetically associated with higher-order compressional reverse-oblique to oblique brittle-ductile high-angle shear zones (Figure 13) commonly located less than 5 km away and best developed in the hanging wall of the major fault (Robert, 1990). Brittle faults may also be the main host to mineralization as illustrated by the Kirkland Lake Main Break, a brittle structure hosting the 25 M oz Au Kirkland Lake deposit (Figure 14). The deposits typically formed late in the tectonic-metamorphic history of the greenstone belts (Groves et al., 2000) and the mineralization is syn- to late-deformation and typically post-peak greenschist facies and syn-peak amphibolite facies metamorphism (cf. Kerrich and Cassidy, 1994; Hagemann and Cassidy, 2000). Most world-class greenstone-hosted quartz-carbonate vein deposits are hosted by greenschist facies rocks. The only exceptions are Campbell-Red Lake (Canada) and Kolar (India) at amphibolite facies.

The greenstone-hosted quartz-carbonate vein deposits are also commonly spatially associated with Timiskaming-like regional unconformities (Figure 15). Several deposits are hosted by (e.g. Pamour and Dome deposit in Timmins) or located next to such a Timiskaming-like regional unconformity (Campbell-Red Lake deposit in Red Lake) (Dubé et al., 2003, in press), suggesting an empirical time and space relationship between large-scale greenstone quartz-carbonate gold deposits and regional unconformities (Hodgson, 1993; Robert, 2000; Dubé et al., 2003).

District scale:

In this section, some of the key geological characteristics of prolific gold districts are presented. The list is far from complete as to the definite reasons why a district like Timmins contains such a large number of world-class gold deposits or why the gold grade in the Red Lake district is overall so high. Only a brief overview is presented here, the reader is referred to key papers such as Hodgson and MacGeehan (1982), Hodgson (1993), Robert and Poulsen (1997), Hagemann and Cassidy (2000), Poulsen et al. (2000), and Groves et al. (2001) among others for more information.

Greenstone-hosted quartz-carbonate-vein deposits are essentially structurally controlled epigenetic hydrothermal deposits. Large gold camps are typically located in greenschist facies Archean greenstone belts and are commonly associated with curvatures, flexures and dilational jogs along major compressional fault zones such as the Destor-Porcupine fault in Timmins or the Larder Lake-Cadillac fault in Kirkland Lake, that have created dilational zones where the hydrothermal fluids were drained (Figure 3). In terms of stratigraphical settings, several gold districts such as Red Lake or Timmins are characterized by the presence of variolitic tholeiitic basalts and ultramafic komatiitic flows intruded by intermediate to felsic porphyry intrusions, and sometimes swarms of albitite or lamprophyre dykes. Timiskaming-like regional unconformities distributed along major faults or stratigraphical discontinuities are also typical characteristics. In terms of hydrothermal alteration, the main characteristic is the presence of large scale iron-carbonate alteration which gives some indication as to the size of the hydrothermal system(s). Protracted magmatic activity with syn-volcanic and syn- to late tectonic intrusions emplaced along structural discontinuities (e.g. Timmins) or surrounding the district (e.g. Red Lake district) appears to be key empirical factors. In many cases, the U-Pb dating of these intrusive rocks indicated that they are older than the mineralization. They have then mainly acted as competent structural trap or induced an anisotropy in the layered stratigraphy, which have influenced and partitioned the strain. In other cases, the intrusive rocks are post mineralization. However, it remains possible that the thermal energy provided by these intrusions may have contributed to large-scale hydrothermal fluid circulation. Presence of other deposit types in the district such as VMS or Ni-Cu deposits is also commonly thought to be a favorable factor (heritage) (cf. Hodgson, 1993).

Knowledge gaps

One of the main remaining knowledge gaps is the tectonic significance and structural evolution of the large-scale faults, which control the distribution of the greenstone-hosted quartz-carbonate-vein deposits. As an example, despite decades of work, the exact location and structural evolution of the Destor-Porcupine Fault in the Timmins district, and its relationship to gold mineralization, remain largely to be established. As well, such a district-scale fault controlling the distribution of the major gold deposits in the Red Lake district remains to be found unless the Cochenour-Gullrock Lake deformation zone (Red Lake Mine trend) (Andrews et al., 1986; Zhang et al., 1997; Dubé et al., 2001a, 2002, 2003) and/or the regional unconformity between the Mesoarchean Balmer and the Neoarchean Confederation assemblages (Sanborn-Barrie et al., 2000, 2001, 2002; Dubé et al., 2003, in press) are marking or represent such a crustal structure.

Deposit scale

The location of higher grade mineralization (ore shoot) within a deposit has been the subject of investigation since the early works of Newhouse (1942) and McKinstry (1948). Ore shoots represent a critical element to take into account when defining and following the richest part of an orebody. Two broad categories of ore shoots are recognized: 1) geometric and 2) kinematic (Poulsen and Robert, 1989; Robert et al., 1994). As outlined by Poulsen and Robert (1989), geometric ore shoots are controlled by the intersection of a given structure (i.e. a fault, a shear zone, or a vein) with a favorable lithological unit, such as a competent gabbroic sill, a dike, an iron-formation or a particularly reactive rock. The geometric ore shoot will be parallel to the line of intersection. The kinematic ore shoots are syn-deformation and syn-formation of the veins and are defined by the intersection between different sets of veins or contemporaneous structures. The plunge of kinematic ore shoots is commonly at a high angle to the slip direction.

Structural traps such as fold hinges or dilational jogs along faults or shear zones are also key elements in locating the richest part of an orebody. However, multiple parameters are commonly involved in the formation of the richest part of an orebody. For example, at the Red Lake Mine, several parameters are believed to have played a key role in the formation of the extremely rich High-grade Zone (Dubé et al., 2002), including: 1) the F2 fold hinge deforming the basalt/komatiitic basalt contact; 2) the carbonatized komatiitic basalt located in the F2 antiform, which acted as a low permeability cap; 3) the iron-rich content of the tholeiitic basalt that allowed precipitation of the arsenopyrite and gold by reaction with the fluids; 4) the more competent nature of the host basalt; 5) several increments of D2 strain; and 6) a new stage of gold mineralization or gold remobilization in extremely-rich fractures that postdated the emplacement of lamprophyre dykes.

As mentioned by Groves et al. (2003), superimposed hydrothermal events often play a key role in the formation of giant gold deposit. This is especially well illustrated at the giant Dome mine in Timmins, where low grade ankerite veins cut across the 2690 Ma Paymaster porphyry (Corfu et al., 1989) (Figure 16A). These ankerite veins have been deformed; they are typically boudinaged and cut by extensional en echelon auriferous quartz veins (Figure 16B, C). As reported in Dubé et al. (2003), the ankerite veins are also present as clasts within the 2679 ± 4 Ma Timiskaming conglomerate in the open pit (Ayer et al., 2003) (Figure 16 D, E), whereas the argillite and sandstone above the Timiskaming conglomerate are themselves cut by folded auriferous quartz veins (Dubé et al., 2003) (Figure 16F). These chronological relationships clearly illustrate the superimposed hydrothermal and structural events involved in the formation of the deposit with post-magmatic carbonate veining pre-dating the deposition of the Timiskaming conglomerate, which in turn precedes the bulk of the auriferous quartz veins mined in the open pit.

Table 1: As of December 31, 2002 District Geological Province Prod.+Reserves (tonnes Au) Resources (tonnes Au)

Timmins	Superior/Abitibi	2,072.9	78.5
Kirkland Lake	Superior/Abitibi	794.8	72.6
Val d'Or	Superior/Abitibi	638.9	171.6
Rouyn-Noranda	Superior/Abitibi	519.6	66.5
Larder Lake	Superior/Abitibi	378.7	14.5
Malartic	Superior/Abitibi	278.7	686.8
Joutel	Superior/Abitibi	61.4	27.5
Matheson	Superior/Abitibi	60.4	9.7
Cadillac	Superior/Abitibi	22.1	25.1
Red Lake	Superior/Uchi	834.5	153.3
Pickle Lake	Superior/Uchi	90.4	8.1
Rice Lake	Superior/Uchi	51.6	25.2
Beardmore-Geraldton	Superior/Wabigoon	123.5	35.1
Michipicoten	Superior/Wawa	41.1	2.8
Mishibishu	Superior/Wawa	26.7	16.8
Goudreau-Lolshcach	Superior/Wawa	8.8	19.6
Flin Flon	Churchill	62.2	12.7
Lynn Lake	Churchill	19.5	14.6
La Ronge	Churchill	3.4	5.6
Keewatin	Churchill-Hearne	7.2	252.4
Yellowknife	Slave	432.8	16.6
MacKenzie	Slave	38.1	286.6
Cassiar	Cordillera	14.9	55.4
Baie Verte	Appalachian/Dunnage	10.3	8.9

From Wikipedia http://en.wikipedia.org/wiki/Superio...

Southwestern Superior province, Wabigoon subprovince

The following study is from Percival (2006): The Wabigoon subprovince has long been recognized as a composite terrane comprising volcanic-dominated domains and consists of distinct western and eastern segments. The Western Wabigoon subprovince is dominated by mafic volcanic rocks with large tonalitic plutons. Volcanic rocks range in composition from tholeiitic to calc-alkaline, and are interpreted to represent ocean floor or plateau and arc environments, respectively. Most of the preserved volcanic rocks were deposited between ca. 2.745 and 2.72 Ga, with rare older rocks, such as the 2.775 Ga Fourbay assemblage of oceanic plateau affinity and minor younger (2.713-2.70 Ga) volcanic-sedimentary sequences. Plutonic rocks range from broadly synvolcanic batholiths composed of tonalite-diorite-gabbro (ca. 2.735-2.72 Ga) to younger granodiorite batholiths and plutons (ca. 2.710 Ga), monzodiorite plutons of sanukitoid affinity (ca. 2.698-2.690 Ga), and plutons and batholiths of monzogranite (2.69-2.66 Ga). Immature clastic metasedimentary sequences are preserved in narrow belts within volcanic sequences. They are commonly younger than the volcanic rocks with local unconformable relationships and geochronological constraints indicating deposition between ca. 2.711 and <2.702 Ga. Detrital zircons >3 Ga indicate old components in source regions. At least two phases of deformation affected supracrustal rocks of the western Wabigoon subprovince, with apparent diachroneity in the onset of deformation from ca. 2.709 Ga in the Lake of the Woods area, to ca. 2.700 Ga in the Sioux Lookout-Savant area in the east. These events involved at least local tectonic inversion, through thrust imbrication and possible formation of nappe-like structures.

The Sturgeon-Savant greenstone belt consists of several tectonostratigraphic packages, including the previously described Jutten assemblage, the ca. 2.775 Ga Fourbay assemblage, and 2.745-2.735 Ga sequence, the Handy Lake and South Sturgeon assemblages. The 2.735 Ga Lewis Lake batholith may have provided the heat source for seawater convection and massive sulfide mineralization. Younger (ca. 2.718 Ga), high Fe, Ti basalt and minor dacite of the central Sturgeon assemblage represent a rifted arc sequence. Associated sedimentary rocks contain both arc (2.745-2.730 Ga) and continental (3.1-2.8 Ga) detritus. Two younger sedimentary sequences complete the stratigraphic record: 1) greywacke-iron formation (ca. 2.705 Ga) of the Warclub assemblage; and 2) sandstone and arkose (<2.698 Ga) of the syn-orogenic Ament Bay assemblage. Two sets of ductile structures postdate <2.704 Ga rocks: 1) north-trending upright folds; and 2) east-trending upright folds and penetrative foliation. Pre-D1 folds have been inferred locally.

The Eastern Wabigoon subprovince is a composite terrane with greenstone belts and intervening granitoid plutons that show variable Mesoarchean (Winnipeg River and Marmion) and oceanic affinity. In the northwest part of the belt the 3.0-2.92 Ga Toronto and Tashota assemblages may represent a continental margin sequence built on the Winnipeg River terrane. Calc-alkaline rocks of the 2.74 Ga Marshall assemblage have small massive sulfide deposits. The central part of the belt is dominated by rocks of oceanic affinity including tholeiitic juvenile pillowed basalt of the 2.78-2.738 Ga Onaman and Willet assemblages and the overlying calc-alkaline 2.725-2.715 Ga Metcalfe-Venus assemblage. Parts of these assemblages contain widespread hydrothermal alteration and host small massive sulfide deposits. Across the southern part of the eastern Wabigoon domain, the 2.78-2.74 Ga calc-alkaline Elmhirst-Rickaby assemblage is possibly built on Marmion-age substrate. Unconformably overlying clastic rocks (Albert-Gledhill and Conglomerate assemblages) were deposited after ca. 2.71 Ga. At least two deformation events affected the eastern Wabigoon domain: east-striking structures (<2.706 Ga) and east-striking, dextral transpressive shear zones. The 2.694 Ga Deeds Lake pluton provides a lower limit on the age of D2 deformation.

So What is in The Future (found at bottom of this web page http://www.prospectorsonline.info/ar...

Independent prospectors and corporate exploration geologists continue to search the Canadian Shield for new deposits of gold. There is every indication that more will be found. As mentioned, the Hemlo deposit was discovered in the 1980s, and the High-Grade Zone of the Red Lake mine was discovered in the 1990s. Recently, a junior exploration company, called Virginia Gold Mines, discovered a large zone of gold mineralization in the James Bay region of northern Quebec; it is known as the lonore discovery (Robertson 2005). In 2001, the company had started reconnaissance of the area around an old copper discovery. In 2002, after various geochemical and geophysical surveys, a boulder was found containing high-grade mineralization-2.7 percent copper and 22.9 grams (0.74 troy ounces) of gold per ton. Subsequent work in 2003 and 2004 located the probable source of the boulder, and several zones of excellent- grade mineralization have been located. It is now likely that this discovery will be one of the newest gold deposits to be developed from the rocks of the Canadian Shield. Where will the next one be?