3
Table 1. Preferred ages of Tertiary Laramide and Paleogene intrusions. Areas with K-Ar dates need to be redated
District Intrusion Age Error Material Method Reference State
Black Hawk Twin Peaks monzonite 75.7 1.3 zircon U-Pb Amato et al. (2017) NM
Black Hawk Argillic alteration 65.3 1.2 mica K-Ar Gerwe (1986) NM
Hillsboro Copper Flat quartz
monzonite
75.9 0.66 hornblende 40Ar/39Ar McLemore et al. (1999) NM
Pinos Altos Pinos Altos stock 78.55 1.75 biotite 40Ar/39Ar Stafford (2024) NM
Pinos Altos Pinos Altos
syenodiorite
72 0.19 groundmass 40Ar/39Ar Stafford (2024) NM
Georgetown Dike 71 40 Ar/39Ar McLemore (1998) NM
Eureka Hidalgo andesite 71.4 0.19 hornblende 40Ar/39Ar Lawton et al. (1993) NM
Lordsburg Lordsburg granodiorite 59.25 0.36 biotite 40Ar/39Ar McLemore et al. (2000) NM
Lordsburg Lordsburg granodiorite 57.03 0.66 K-feldspar 40Ar/39Ar Stafford (2024) NM
Santa Rita Santa Rita stock 59.05 0.15 biotite 40 Ar/39Ar NMBGMR Unpublished NM
Santa Rita Supergene Alteration 34.3–
29.6
alunite K-Ar Cook (1994) NM
Fierro-
Hanover
FierroHanover stock 58.3 0.07 biotite 40Ar/39Ar McLemore et al. (1995) NM
Copper Flat (Grant
County)
Copper Flat
granodiorite
57.5 0.7 zircon U-Pb Mizer et al. (2015) NM
McGhee
Peak
Buried quartz
monzonite
57.28 0.65 K-feldspar 40 Ar/39Ar Stafford (2024) NM
Burro Mountains
(Tyrone)
Tyrone stock 55.2 0.6 biotite 40Ar/39Ar NMBGMR Unpublished NM
Burro Mountains
(Tyrone)
Supergene alteration 22.5–
4.5
alunite 40Ar/39Ar Leveille and Stegen (2012) NM
Tyrone Tyrone stock 58–54 zircon U-Pb (Stegen et al., 2024) NM
Lone Mountain Lone Mountain stock 50.6 1.9 biotite K-Ar More and Moran (2006) NM
Camel Mountain -
Eagle’s Nest
Eagle’s Nest diorite 40.19 0.04 biotite 40Ar/39Ar Stafford (2024) NM
Cooks Peak Rubio Peak Formation 38.95 0.13 biotite 40Ar/39Ar Schwenk
Unpublished
NM
Cooks Peak Granodiorite 39.1 0.1 zircon U-Pb (Amato et al., 2018 NM
Victorio Victorio Granite 36.13 0.07 muscovite 40 Ar/39Ar Donahue (2002) NM
Tres Hermanas Tres Hermanas quartz
monzonite
35.94 0.12 biotite 40Ar/39Ar Stafford (2024) NM
Tres Hermanas Tres Hermanas quartz
monzonite
35.01 0.23 groundmass 40Ar/39Ar Stafford (2024) NM
Eureka Eureka andesite? 35.52 0.12 groundmass 40Ar/39Ar Stafford (2024) NM
Camel Mountain -
Eagle’s Nest
Prospect Hills granite 35.2 3.4 hornblende 40 Ar/39Ar Stafford (2024) NM
McGhee Peak Quartz monzonite at
surface
31.38 0.05 groundmass 40Ar/39Ar Stafford (2024) NM
San Simon Granite Gap granite 33.65 0.2 biotite 40Ar/39Ar McLemore et al. (1995) NM
Apache No.2 and
Fremont
Chapo Formation 30.66 1.5 K-Feldspar K-Ar Deal et al. (1978) NM
Safford Eocene stocks 59–54 zircon U-Pb (Stegen et al., 2024) AZ
Morenci Eocene stocks 59–54 zircon U-Pb (Stegen et al., 2024) AZ
Santa Rita Eocene stocks 59.905–
57.744
0.028-
0.035
zircon U-Pb (Gaynor et al., 2024) NM
Hummingbird Mine
Burro Mountains
Burro Mountains
Diorite
70.7 1.1 zircon U-Pb (Amato &Boullion,
2008) Average date
NM
Table 1. Preferred ages of Tertiary Laramide and Paleogene intrusions. Areas with K-Ar dates need to be redated
District Intrusion Age Error Material Method Reference State
Black Hawk Twin Peaks monzonite 75.7 1.3 zircon U-Pb Amato et al. (2017) NM
Black Hawk Argillic alteration 65.3 1.2 mica K-Ar Gerwe (1986) NM
Hillsboro Copper Flat quartz
monzonite
75.9 0.66 hornblende 40Ar/39Ar McLemore et al. (1999) NM
Pinos Altos Pinos Altos stock 78.55 1.75 biotite 40Ar/39Ar Stafford (2024) NM
Pinos Altos Pinos Altos
syenodiorite
72 0.19 groundmass 40Ar/39Ar Stafford (2024) NM
Georgetown Dike 71 40 Ar/39Ar McLemore (1998) NM
Eureka Hidalgo andesite 71.4 0.19 hornblende 40Ar/39Ar Lawton et al. (1993) NM
Lordsburg Lordsburg granodiorite 59.25 0.36 biotite 40Ar/39Ar McLemore et al. (2000) NM
Lordsburg Lordsburg granodiorite 57.03 0.66 K-feldspar 40Ar/39Ar Stafford (2024) NM
Santa Rita Santa Rita stock 59.05 0.15 biotite 40 Ar/39Ar NMBGMR Unpublished NM
Santa Rita Supergene Alteration 34.3–
29.6
alunite K-Ar Cook (1994) NM
Fierro-
Hanover
FierroHanover stock 58.3 0.07 biotite 40Ar/39Ar McLemore et al. (1995) NM
Copper Flat (Grant
County)
Copper Flat
granodiorite
57.5 0.7 zircon U-Pb Mizer et al. (2015) NM
McGhee
Peak
Buried quartz
monzonite
57.28 0.65 K-feldspar 40 Ar/39Ar Stafford (2024) NM
Burro Mountains
(Tyrone)
Tyrone stock 55.2 0.6 biotite 40Ar/39Ar NMBGMR Unpublished NM
Burro Mountains
(Tyrone)
Supergene alteration 22.5–
4.5
alunite 40Ar/39Ar Leveille and Stegen (2012) NM
Tyrone Tyrone stock 58–54 zircon U-Pb (Stegen et al., 2024) NM
Lone Mountain Lone Mountain stock 50.6 1.9 biotite K-Ar More and Moran (2006) NM
Camel Mountain -
Eagle’s Nest
Eagle’s Nest diorite 40.19 0.04 biotite 40Ar/39Ar Stafford (2024) NM
Cooks Peak Rubio Peak Formation 38.95 0.13 biotite 40Ar/39Ar Schwenk
Unpublished
NM
Cooks Peak Granodiorite 39.1 0.1 zircon U-Pb (Amato et al., 2018 NM
Victorio Victorio Granite 36.13 0.07 muscovite 40 Ar/39Ar Donahue (2002) NM
Tres Hermanas Tres Hermanas quartz
monzonite
35.94 0.12 biotite 40Ar/39Ar Stafford (2024) NM
Tres Hermanas Tres Hermanas quartz
monzonite
35.01 0.23 groundmass 40Ar/39Ar Stafford (2024) NM
Eureka Eureka andesite? 35.52 0.12 groundmass 40Ar/39Ar Stafford (2024) NM
Camel Mountain -
Eagle’s Nest
Prospect Hills granite 35.2 3.4 hornblende 40 Ar/39Ar Stafford (2024) NM
McGhee Peak Quartz monzonite at
surface
31.38 0.05 groundmass 40Ar/39Ar Stafford (2024) NM
San Simon Granite Gap granite 33.65 0.2 biotite 40Ar/39Ar McLemore et al. (1995) NM
Apache No.2 and
Fremont
Chapo Formation 30.66 1.5 K-Feldspar K-Ar Deal et al. (1978) NM
Safford Eocene stocks 59–54 zircon U-Pb (Stegen et al., 2024) AZ
Morenci Eocene stocks 59–54 zircon U-Pb (Stegen et al., 2024) AZ
Santa Rita Eocene stocks 59.905–
57.744
0.028-
0.035
zircon U-Pb (Gaynor et al., 2024) NM
Hummingbird Mine
Burro Mountains
Burro Mountains
Diorite
70.7 1.1 zircon U-Pb (Amato &Boullion,
2008) Average date
NM