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'i <br /> <br />GOfl) IfIIl PROTECT <br />PAGE 3-! <br />3- GEOIAGICAL SETTING <br />'I <br />,~ <br />'I <br /> <br />'I <br />The Gold Hill, Central, Magnolia, Jamestown and Sugarloaf mining <br />districts aze all extensions of an oval shaped granite batholith to the <br />south. This Tertiary intrusion is in contact with quartz biotite schists <br />of the Idaho Springs Formation, Precambrian in age, neaz the town <br />of Gold Hill. The schists aze cut by a strong system of north-westerly <br />trending faults locally known as "breccia reefs". These have a signifl- <br />cant influence on the distribution of the auriferous veins in the <br />districK. <br />'I <br />i <br />1 <br />The important ore veins lie within 2,000 feet of one of the breccia <br />reefs which suggests that the reefs were deep channels for the auri- <br />ferous solutions. The northeast trending veins were open structures for <br />the hydrothermal solutions. <br />The three most important breccia reefs aze the Hoosier, Maxwell and <br />Livingstone. All aze parallel, about 2 miles apart, and outcrop over a <br />20 mile strike length. Two other reefs, the Fortune and the Poorinan, <br />have a more east west vend. Gold Hill occurs at the intersection of <br />the Hoosier and Fortune reefs. This is shown in Figure 2. <br />The most important structural controls for ore grade mineralisation <br />are as follows: <br />1- The junction of a vein with a breccia reef such as the <br />Ingram, Victoria and Emandpation veins at their <br />intersection with the Hoosier Ree£ <br />2- The junction of two productive veins. <br />3- The junction of a productive vein with a barren fissure. <br /> <br /> <br /> <br />'I <br />The veins are mainly infilled fault fissures and nearly all dip to the <br />northwest with a northeasterly strike and are from 1 to 5 feet thick. <br />There are two main productive sets of veins. An earlier, more <br />important, set is filled by gold-silver telluride with a NNE strike and <br />a second set, striking ENE, is filled by lead-silver, pyritic and native <br />gold. These veins vary in length from 200 feet to almost a mile with <br />widths between 1 and 5 feet but fracture zones from 10 to 30 feet <br />wide do occur. <br />R. W. Turner C.Eng. <br />Consulting Mining Engineer <br />