Goldmine

n.capable, hopefulplayful

What it means

A source containing an unusually rich supply of valuable information, ideas, or opportunity.

Reach for it when describing abundant potential while making clear what the value consists of

The oral-history archive is a goldmine for local researchers.

playful
bonanza
a sudden abundance or commercial gain creates excitement
not when Bonanza suggests a windfall and fits poorly for value requiring years of work.
playful
mother lode
the source seems to contain the main concentration of value
not when Mother lode is mining slang and can sound clichéd or speculative.
everyday
windfall
unexpected benefit arrives with little prior planning
not when A goldmine may demand sustained extraction, unlike a windfall.
warm
treasure trove
many valuable discoveries are already present
not when Treasure trove is decorative language and may overstate routine records.
professional
rich source
measured prose should identify abundant useful material
not when Rich source is accurate but lacks the exceptional promise of goldmine.
formal
trove
a collected store of valuable objects or information is meant
not when Trove implies a discovered collection rather than an ongoing opportunity.
literary
reservoir
stored abundance can be drawn on over time
not when Reservoir suggests capacity but not exceptional worth.

goldmine of information
The annotated catalog is a goldmine of information for conservators.
data goldmine
The survey could become a data goldmine if consent and access remain clear.
potential goldmine
The neglected seed bank is a potential goldmine for climate research.

Goldmine is metaphorical and does not prove financial value. Name the valuable material or opportunity.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.