Geology and Structure
The Pamlico Project lies in the western Great Basin within the regional Walker Lane structural lineament and is crossed by the E – NE trending Pancake Range Lineament described by Erken et al. in USGS Professional Paper 986. Numerous other mines and mining districts are found in and near the Walker Lane and along the Pancake Lineament. Nearby mines include Round Mountain, Borealis, Aurora, and Bodie, which together form an arcuate belt of mines and mining districts roughly centered on Pamlico. Other major mines and mining districts of the Walker Lane include the Comstock Lode, Denton Rawhide, Goldfield, Tonopah, Paradise Peak, Yerington and many more.
The Walker Lane is a zone of NW striking right-lateral (dextral) strike slip movement parallel to and related to the same geologic forces that generate the San Andreas Fault system. Related NS to NE trending sinusoidal tensional faults provide additional primary structural control for mineralization, including the high-grade Merritt zone. EW structures related to the Pancake Range lineament provide additional structural control for mineralization at Pamlico.
The regional structural pattern is replicated at the district and mine scale where dominant mineral trends observed strike NW, NS and EW with the highest grade surface rock sample at 684g/T Au originating from an EW trending vein.
Regional Host Rocks and Stratigraphy
Paleozoic Rocks including: -Ordovician slate, chert, limestone, and sandstone. -The Permian Diablo Fm. (sandstone and grit).
Mesozoic rocks -Volcanic and sedimentary rocks include the Triassic Excelsior Fm. (volcanic, clastic and tuffaceous rocks, and intrusive rhyolite domes), the Triassic Luning Fm. (limestone, dolomite, and shale), the Triassic Gold Range Fm. (volcaniclastic intermediate to felsic debris flows and airfall, time equivalent to volcanic member of Luning Fm., the Triassic Gabbs and Sunrise Formations (shale and limestone), Jurassic Dunlap Fm. (sandstone, conglomerate, and volcanic rocks). Intrusive rocks include Cretaceous diorite, quartz monzonite, granodiorite and granite.
Tertiary rocks including: -pre-Esmeralda volcanic rocks (intermediate to felsic volcanic rocks) the Tertiary Esmeralda Fm. (shale, conglomerate, and rhyolitic tuff). -Intermediate volcanic rocks (rhyodacite and andesite flows and tuffs) and felsic volcanic rocks (rhyolite and quartz latite tuffs) of uncertain affiliation.
Quaternary mafic volcanic rocks (trachybasalt and latite flows). Locally small mafic dikes appear to be feeders to the mafic volcanism.
Pamlico district and Property Geology
Within the Pamlico District, the oldest exposed rocks of the Excelsior Formation are of probable Permian age. These are unconformably overlain by rocks of the complex and inter-fingering Luning and Gold Range Formations. The Dunlap formation unconformably overlies the Excelsior, Luning and Gold Range Formations. Tertiary to Quaternary trachybasalt to latite and basalt flows outcrop in a distal circular outcrop pattern that results in a dome like appearance to the general geology of the district.
The dominant lithologic units of the Pamlico property as described by Archbold and Paul are:
The Permian age, Excelsior formation was named by Muller and Ferguson (1936) for exposures approximately 6 miles SW of Pamlico. As described by Archbold and Paul, at Pamlico, rocks assigned to the Excelsior Formation are composed of three recognizable lithologic types, consisting of latite tuff and agglomerate, rhyolite and laminated possibly waterlain rhyolitic tuff.
Luning and Gold Range Formations
The Luning and Gold Range Formations are complex, time equivalent inter-fingering formations deposited in a shallow marine to subaerial, environment. Together the formations have an estimated thickness of 2,000 feet.
The Luning Formation is an Upper Triassic limestone dominated formation. In the Pamlico District, the Luning Formation rests unconformably on the Excelsior Formation and consists of a lower limestone up to 100 feet thick that occurs as discontinuous scattered lenses and pods formed in shallow lagoons between erosional highs of the Excelsior Formation. The overlying middle member is equivalent to the Gold Range Formation and is composed of sedimentary breccia, argillite, conglomerate, volcanic flows, pyroclastics and waterlain tuff of apparent andesitic composition. The upper member of the Luning Formation is composed of 1,000 feet of thin to medium bedded limestone and shaly limestone with rare shale, silt and mudstone.
The Gold Range Formation is characterized as a heterogeneous wedge of sedimentary breccia, argillite, conglomerate and andesitic to rhyolitic flows and pyroclastic units that correlate with the middle clastic unit of the Luning Formation. Lying unconformably above the Excelsior Formation and conformably below the upper limestone unit of the Luning Formation, the Gold Range Formation is characterized by rapid lateral facies changes and is estimated to be 800 to 1,000 feet thick at Pamlico.
Gabbs and Sunrise Formations
The Gabbs Formation of late Triassic and the Sunrise Formation of Early Jurassic age outcrop in the Pamlico district east of Newrange’s Pamlico property and conformably overlie Luning Formation. The two formations are nearly identical in appearance without a noticeable break in depositional style and rely exclusively on paleontological evidence to distinguish between them. In the Pamlico district these formations consist of light brown to light grey shaly limestone.
The Dunlap Formation of early Jurassic age unconfirmable overlies the Sunrise, Luning, Gold Range and Excelsior Formations. The Dunlap Formation is most widely exposed on the higher peaks south of the Pamlico property. In the Pamlico district, the Dunlap Formation consists of dark grey, locally agglomeratic rock with andesite fragments up to a foot in diameter in a similar matrix. It resembles rocks of the Gold Range Formation, but can be distinguished by its greater uniformity and absence of shales and other lithologies of the Gold Range Formation.
Regional structure comprises Basin and Range block faulting that has been overprinted by NW trending dextral (right lateral) strike slip and oblique slip faults, and associated N-NW trending dextral synthetic faults of the Walker Lane together with N-S trending normal faults and E-W trending compressional (strike slip) faults related to the Pancake Range structural zone.
At the property scale, structure includes Tertiary NW striking, right lateral strike slip and right oblique slip faults related to the Walker Lane with sub-parallel fracture cleavage and coeval sinusoidal, NS and NE striking first and second order extensional “en echelon” or “gash” faults. Large EW to NE trending right oblique (dextral) strike slip faults related to the Pancake Range Lineament transect the property with little if any apparent offset by, or of structures related to the Walker Lane and are probably coeval.
Intense folding is evident everywhere in the carbonate sediments of the upper Luning Formation. It is likely that unrecognized overturned folds are present within the sedimentary package and potentially provide important controls for localization of mineralization in these sediments.
Mineralization and Alteration
At Pamlico, mineralization occurs in a complex structural environment along NW, N-NE trending structures related to the Walker Lane and N-NE to E-W trending structures related to the Pancake Range Lineament. Mineralization structures vary from nearly vertical to nearly horizontal dips. Thrust faults and / or strata-conformable breccias are mineralized proximal to these high angle structures. Alteration and mineralization is reported in rocks ranging in age from Permian to upper Tertiary age.
The bulk of historic production from the property originated from mineralized structures in brittle rhyolite of the Permian age Excelsior Formation with lesser amounts coming from the Gold Range and Luning Formations of Triassic age. Archbold, (1970) observes: “The upper limestone member of the Luning Formation is highly silicified up to 100 feet outward from faults in the central part of the district.” This silicification coupled with historic production from structures in these limestone units clearly demonstrates ascending mineralizing fluids circulating in structures cutting both the Gold Range and underlying Excelsior Formations. Potential exists in these structures for high-grade structurally controlled narrow vein gold mineralization at depth similar to that currently being mined at Midas, Hollister and Fire Creek and for sediment hosted mineralization in permeable zones such as axial planes of folds and strata-conformable breccia zones in limestone of the upper Luning Formation, where surface samples have yielded values ranging from 1.3 to 9.5g/T Au.
At the scale of individual mines, veins with variable strike and dip are common suggesting potential for numerous favorable structural intersections. Within and around the structurally controlled veins hosted in volcanic rocks intense clay alteration and strong bleaching are evident. Alteration envelopes of intense clay alteration exceeding one meter occur within broader alteration envelopes of silica flooding and bleaching related to vein swarms that may exceed 2.6 kilometers along strike and 750 meters in width.
Individual veins typically consist of a combination of crystalline and massive quartz commonly with frothy quartz with earthy, powdery iron and manganese oxides. Oxidation levels appear to become progressively deeper from south to north with sulfides including pyrite / marcasite and galena becoming noticeably more abundant to the south.
Gold mineralization appears to be spatially associated with concentrations of iron and manganese oxides. Within the gold rich zones, gold to silver ratios are usually in the 10:1 to 1:1 range. A separate low-grade silver dominant event is evident, but where sampled is uniformly low grade.
Overall, gold mineralization is geochemically associated with mercury and lead with correlation coefficients of 41.4% and 31.9%, respectively. In the high-grade subset of samples that contain more than 10 g/T Au, mercury and lead exhibit correlation coefficients of 89% and 59.4% respectively. Interestingly, in this same subset, calcium shows the highest correlation with gold at 93.8%. Nickel and phosphorus exhibit 59.7% and 46.8% coefficients of correlation, while molybdenum shows a strong inverse correlation with gold at -48.4% in this subset. While many epithermal veins contain elevated concentrations of calcite as gangue mineral, there is no crystalline calcite observed in the veins at Pamlico. The strong association of calcium with gold at Pamlico is thought to be related to the secondary development of caliche in the near-surface over the altered vein zones as discussed below. While not genetically related to the gold mineralization, this high correlation of gold and calcium / caliche is likely to be a very useful prospecting and exploration tool in the search for new veins that have yet to be discovered.
Alteration associated with mineralized structures manifests itself as zones of quartz veining and silica flooding ranging from one to ten meters wide in volcanic rocks and reported as up to 30 meters wide in the sediments of the upper Luning Formation.