Minerals of Golden Horn Batholith, Okanogan County, Washington

GOLDEN HORN BATHOLITH
Washington Pass, Okanogan County, Washington

LOCALITY IMAGES

GEOLOGY
Golden Horn Batholith - Tertiary. The Golden Horn Batholith is a highly evolved alkaline (Sodium rich) granite that contains a high concentration of REE (rare earth elements) and other incompatible elements (such as zirconium). During fractional crystallization of the magma, the residual liquid became increasingly enriched in these incompatible elements as the rock-forming mineral phases that were crystallizing rejected them. Late stage volatile rich fluids carrying this highly fractionated chemistry precipitated a suite of rare minerals in miarolitic cavities within the alkaline granite. The Golden Horn Batholith is the type locality for three of these rare mineral species, zektzerite- NaLiZrSi₆O₁₅, the REE mineral, okanoganite- (Na,Ca)₃(Y,Ce)₁₂Si₆B₂O₂₇F₁₄ and calciohilairite- CaZr[SiO ₃]₃·3H₂O. Over 50 mineral species have been identified at this locality, with a great potential for new mineral discoveries.

Collecting is within the Okanogan National Forest. The host granite covers a vast area of of alpine terrain.

MINERALS (incomplete list) CLICK for COMPLETE LIST


*Arfvedsonite-	Na₃(Fe,Mg)₄(Fe,Al)Si₈O₂₂(OH)₂ - Occurs as brilliant black prismatic crystals up to many centimeters in length in mariolitic cavities and and as acicular aggregates in pegmatitic portions of the alkali granite. Also occurs as inclusions within smoky quartz.
*Astrophyllite-	(K,Na)₃(fe,Mn)₇Ti₂Si₈O₂₄(O,OH)₇ - Occurs as bronze micaceous bladed aggregates with metallic luster in some miarolitic cavities and as massive aggregates in pegmatitic portions of the alkali granite. Some smoky quartz crystals contain brilliant thin transparent red blades of astrophyllite.
*Bastnaesite-(Ce)	CeCO₃(OH,F) - Occurs as mm-scale orange prismatic hexagonal crystals.
* Microcline-	KAlSi₃O₈ - Occurs as opaque white crystals to 1 cm lining miarolitic cavities.
*Okanoganite-	(Na,Ca)₃(Y,Ce)₁₂Si₆B₂O₂₇F₁₄ - Occurs as rare tan to peach colored crystals typically less than 1 mm.
* Quartz-	SiO₂ - Occurs as milky to smoky crystals lining pockets up to a few decimeters in length. Some quartz is gemmy with a smoky-amethyst coloration. Inclusions of arfvedsonite, astrophyllite, or other species are common.
* Riebeckite-	Na₂Fe⁺³₂Fe⁺²₃(Si₈O₂₂)(OH)₂ - Occurs as acicular opaque dark blue-green crystals. Some riebeckite is absestiform.
* Siderite-	FeCO₃ - Occurs as mm-scale rhombohedra in miarolitic cavities.
* Zektzerite-	NaLiZrSi₆O₁₅ - Occurs as white to gemmy pink crystals to 3.7 cm. Zektzerite fluoresces green under short-wave ultraviolet light.
* Zircon-	ZrSiO₄ - Individual crystals to about 1 cm occur within some cavities. Specimens are brown, lusterous, and exhibit tetragonal prism faces.