Marietta Project

(The following text has been extracted from the 43-101 technical reports)

Located in the prolific Walker Lane Mineral Belt of West Central Nevada, where past production has yielded more than 35 million gold equivalent ounces.

Summary:

The Marietta Project area is situated in the Marietta Mining District of Mineral County, Nevada. The project is comprised of 13 patented lode claims as well as 118 unpatented lode mining claims. 

The Marietta Mining District is located in the east-central Excelsior Mountains.  The Excelsior Mountains form an irregular range which extends generally east and west, in contradiction to the typical mountain ranges of the Walker Lane mineral belt that hosts the Marietta Project.

The northwest-trending Walker Lane mineral belt of the western Basin and Range hosts numerous other gold and silver deposits.  The mineral belt measures approximately 600 km long by 130 km wide and is defined as a NW-trending structural corridor controlling numerous high and low sulfidation gold and silver deposits including Comstock and Round Mountain.  

It is estimated that the Marietta Mining District contains in production and resources over 46 million ounces of gold and over 436 million ounces of silver. The deposit types at the Marietta Project are high grade medium width veins with the dominant minerals of quartz and iron oxides and sulfides.  The Marietta Project contains several silver-gold exploration targets as well as a copper exploration target. 

An exploration program of geological mapping, soil sampling, underground sampling, and surface drilling has been carried out, and analysis of the results is ongoing.  Azteca Gold is currently inactive on this project, and its carrying costs to keep it are low.

Location:

The Marietta Project is located in the Marietta Mining District of Mineral County, Nevada. The area is accessed from Reno, Nevada, via Interstate 80 , to U.S. Highway 50 east, to U.S. Highway 95 south, to Nevada State Route 360 west, to the Marietta turn off, then approximately 9 miles (14.5 km) west on an improved dirt road to the town site of Marietta.  From the town site of Marietta unimproved dirt roads lead north into the mines area.

History:

Mineralization was discovered in what became the Marietta Mining District in the 1860’s, making it the third oldest mining district in Mineral County.  The district is most frequently referred to as the Silver Star District in published literature.  More recent publications refer to it as the Marietta Mining District, which also now includes a number of other districts and sub-districts situated in the Excelsior Mountains (i.e. Silver Star, Gold Range, Mina, Black Mountain, and Douglas).  Mining started in the 1870’s and continued intermittently through the 1980’s, but by and large had ceased by 1956.  Approximately $2 million in total production in silver, lead, copper, gold, and tungsten was reported by 1939.  Just over half of this value was in tungsten.  During the period of mining activity numerous shaft, adits, and declines were driven into altered rock.  Production amounts attributable to the Marietta Mines are for the most part unrecorded, but the amount and size of the workings suggest some production was made.  Old workings, varying in age from the 1870’s to about the 1950’s (locally more recent) are found approximately two miles north-northwest of the Marietta Mines. These workings exploit silver-lead veins that trend generally northwest.

A geophysical study conducted in 2005 utilized gravity and magnetic surveys.  The regional magnetic data appear to show a regional contact structure trending northwest-southeast.  Additionally, the gravity data suggests a strong gravity high approximately where the Marietta ground magnetic survey is located.

The surveys identified numerous drill targets.

Geology:

The Marietta Project is situated within the northwest-trending Walker Lane mineral belt of the western Basin and Range province.  The Walker Lane is characterized by northwest trending en echelon right-lateral strike-slip faults that have tilted and rotated structural blocks throughout its extent.  There are a number of mining districts and mineral deposits located within the Walker Lane Structural Zone including the Comstock Lode, Tonopah District, Goldfield District, and the Rawhide, Paradise Peak, and Bullfrog Mines.  These districts have produced significant quantities of precious and base metals over the past 125 years.

Regionally, Triassic to Jurassic age argillite, calcareous sandstone and limestone has been intruded by stocks and sills of Cretaceous age.  Hornfels and skarns have developed as large aureoles around the intrusives.  The region is characterized by low angle thrusts and high angle normal and strike slip faults.

The oldest units exposed in the Marietta Mining District consist of the Permian metavolcanic and metasedimentary rocks of the Mina Formation and the Black Dike Formation. The Mina Formation and the Black Dike Formation are interpreted to be in thrust contact with the Jurassic Dunlap Formation. The Permian formations are interpreted to be the upper plate of the thrust sheet while the Jurassic Dunlap Formation is interpreted to be the lower plate.  Between Moho Mountain and the Marietta Mines, both the upper and lower formations have been intruded by dikes and masses of granodiorite, quartz monzonite, and granite porphyry.  To the west of the Marietta Project the Excelsior Mountains have been underlain by Cretaceous granitic rocks. West of Moho Mountain a small area of the district is covered by Tertiary andesite.

The stratigraphy at the Marietta Project is composed of two rock types; metamorphosed volcanic rocks below and weakly metamorphosed sedimentary rocks above.  The upper plate consists of bedded to massive sequences of chert pebble conglomerate.  The unit is variously purple, violet or light green to light gray, with local interbeds of laminated to thick bedded, light brown to gray sandstone.  Epidote crystals are present on some fractures.  These siliciclastic rocks form the majority of the low ridges in the mapped area.  The unit is very broken and locally crushed, particularly near low angle structures.   A unit identified as calc-silicate is found on the western edge of the project area and occurs between conglomerate and sandstone units.  The contact is variously sheared and/or brecciated.  The calc-silicate rocks are fine grained, dark green and locally calcareous.  This unit contains bedding defined by concentrations of various minerals and forms bold outcrops.  Colluvium covers most slopes with up to 3 meters of material.  Alluvium is generally thin in many of the small draws but can be in excess of 10 m thick in the larger valleys.  Alluvial fans of unknown thickness have formed at the front of the range.  The lower plate metavolcanic sequence consists of two types of rock; a trachytic unit composed of plagioclase crystals (to 2 cm) in a fine grained matrix and a fine grained massive flow unit.  The trachytic unit is dark green, except where it is hydrothermally altered. Local concentrations of epidote are found on fractures and veins.

All rocks in the project area have been subjected to regional greenschist facies metamorphism prior to hydrothermal alteration.  Hydrothermal alteration has produced differing mineralogy between the two principal lithologies.  Alteration within the sedimentary rocks is characterized by limonitic staining along structures.  In areas where alteration is intense, local and rarely larger areas of silicification are observed.  Silicification is well developed in areas of open spaced brecciation.  In silicified rocks, goethite veins up to 1 cm thick are present along with hematite staining.  Occasionally druzy quartz is present along bedding.  There are two alteration types present. The primary type is quartz-sericite-pyrite (QSP) alteration.  This alteration is recognizable by the outcrops of dark brown to black bouldery material.  The primary mineral make up of this material is sericite and/or kaolinite, goethite, and quartz with common concentrations of black manganese oxides, red hematite and rarer copper carbonates (azurite and malachite).

Underlying this zone is a thick zone of white kaolinite.  Low angle shears are frequently present in this material.  Iron oxide stains are common and in many areas cause the white clays to turn pink. Goethite replaced pyrite cubes and striated modified pyrite cubes to 5 mm are common in the white clays.  This style of alteration is found everywhere at the contact between the sedimentary rocks and the volcanic rocks and in most areas is 1 m or less in thickness. Where it underlies the QSP alteration, the kaolinite alteration is in excess of 10 m thick.  Copper oxides are most readily developed in unaltered or only weakly altered metavolcanic rocks, often below areas of argillic alteration.  Local concentrations yield malachite and azurite crystals to 2 mm.  The highest concentration of malachite was found in unaltered dark green meta-volcanic rocks northeast of the main mining areas. Quartz veins are found throughout the area concentrated in areas of intense hydrothermal alteration.  The veins are primarily massive white quartz and may be layered with pyrite and chalcopyrite.  Pyrite and chalcopyrite are often found dispersed in unaltered metavolcanic rocks, usually in pod-shaped bunches of subhedral and euhedral crystals.  These sulfides are often altered to goethite and/ or malachite with malachite forming green stains haloing the sulfide pods.

Structure:

The Marietta Project area is cut by numerous small and large structures.  The area can be divided simplistically into low angle structures (with dips less than 50 degrees) and high angle structures (dips greater than 50 degrees).  The low angle structures likely formed earliest. They are common in both the sedimentary unit and the volcanic unit. These structures are seldom planar.  Often they are discontinuous and exhibit complex curved surfaces.  Low angle structures in the sedimentary package are characterized by crushed rock and are frequently accompanied by a limonitic clay core.  In the volcanic rocks, the low angle structures often exhibit plastic deformation and hydrothermal alteration.  Kaolinite or sericite clays are frequently developed.

The high angle structures are characterized by three principle strike directions: north-northwest, west-northwest, and east-northeast.  The most important strike direction is the north-northwest set which acts as the primary feeders and veins. The dips vary in direction and degree.  Many of the sulfide bearing quartz veins have this orientation as well. The principle mineralized zone also trends north-northwest out of the central alteration area.  The west-northwest trending set of high angle structures cut and offset the low angle structures.  These faults are recognized in underground exposures by crush zones and minor clay development.

Mineralization:

At least three types of mineralization have been identified at the Marietta Project.  There are two gold systems, and a third which is a copper-rare earth system.  Mesothermal quartz veins have been identified with up to 49.2 g/t (1.435 opt) gold (up to 66 g/t (1.925 opt) from surface samples). These are cross-cut by a later, high angle shear hosted, epithermal gold system with values to 17.3 g/t (0.504 opt) gold. The strike length of the epithermal gold system is greater than 1000 meters.  The extent of the high-grade quartz vein system has not yet been determined.  Gold mineralization is almost entirely hosted within the metamorphosed sandstones and conglomerates located in the central and western portion of the region.

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