First published use for a quartz monzonite exposed over a 6 sq mi area in the Little Ajo Mountains which lie in T12S, Rs6 and 7W, Pima Co, AZ in the Basin-and-Range province. Intent to name and designation of a type not stated. Probably named for New Cornelia mine. Is resistant to erosion; forms steep rugged slopes. Intrudes Concentrator volcanics (new), Cardigan gneiss (new), and Chico Shunie quartz monzonite (new). Locomotive fanglomerate (new) and Daniels conglomerate (new) were deposited on it. Consists of fine-grained, equigranular quartz diorite (border facies) through equigranular quartz monzonite and porphyritic quartz monzonite to aplite and pegmatite. The border facies is gray, fine-grained, and plagioclase, hornblende, biotite recognized in hand specimen. Equigranular facies has pinkish-gray potash feldspar, white plagioclase, quartz, biotite, hornblende. Porphyritic facies is gray, has plagioclase, orthoclase, quartz, sphene. Has been altered. Chemical analyses. Age not known. Assigned to the early? Tertiary?. Geologic map.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Mapped in Ajo 15' quad (scale 1:62,500), in area surrounding New Cornelia mine (scale 1:6,000), and in Ajo mining district (scale 1:1,200), all of Pima Co, AZ. Dioritic border facies is shown separately. Assigned early(?) Tertiary age.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

[Cornelia Quartz Monzonite is informally referred to as New Cornelia stock.] Samples collected from medium-grained quartz monzonite in northwestern corner of Ajo copper mine, in NW/4 NE/4 sec. 27, T. 12 S., R. 6 W., Ajo 15-min quadrangle, Pima County, Arizona, yielded K-Ar ages of 63.6 +/-1.9 Ma and 62.6 +/-1.9 Ma (biotite), and 62.2 +/-1.9 Ma. Samples collected from medium-grained equigranular quartz monzonite west of Ajo, in NE/4 SE/4 sec. 21, T. 12 S., R. 6 W., Ajo 15-min quadrangle, Pima County, Arizona, yielded K-Ar ages of 19.6 +/-3.5 Ma (hornblende) and 19.1 +/-1.3 Ma (biotite); these ages probably reflect time of alteration. [Note this area west of Gibson Arroyo fault is informally called Cardigan Peak pluton (middle Tertiary age) by Hagstrum, 1987.]

Source: Modified from GNU records (USGS DDS-6; Menlo GNULEX).

Geographically restricted to plutonic rocks east of Gibson Arroyo fault. Age is changed from early(?) Tertiary to: Late Cretaceous and early Tertiary based on K-Ar ages of 39.2 +/-1.9 and 42.5 +/-1.7 Ma (this report) and 64.2 +/-1.9, 65.2 +/-1.9, 63.8 +/-1.9, and 62.9 +/-1.9 Ma (originally from McDowell, 1971). [Plutonic rocks west of fault are mid-Tertiary age and informally called Cardigan Peak pluton in this report. Cornelia Quartz Monzonite is informally referred to as Cornelia pluton.]

Source: GNU records (USGS DDS-6; Menlo GNULEX).