The phrase "an extremely valuable source" is correct and usable in written English.
You can use it when referring to a person, document, or resource that provides significant and beneficial information or insights.
Example: "The research paper proved to be an extremely valuable source for my thesis on climate change."
Alternatives: "a highly beneficial resource" or "an invaluable reference".
His newspaper remains an extremely valuable source for the study of the political and economic controversies in the United States of his day.
While these documents, which include scripts, letters, and snapshots, may not fully answer these questions of attribution, they would certainly constitute an extremely valuable source of information for any further research on Reville and, particularly, her early career.
Without doubt, DNA sequence data are an extremely valuable source of information to infer phylogenetic relationships.
The enormous structural information contained in the protein data bank[ 186] provides an extremely valuable source for the structure-based design of novel ligands.
These samples are an extremely valuable source for molecular biology studies, since they have been annotated with varied information on disease states and patient follow-up, such as disease progression in cancer and prognosis/survival data.
Cassava leaves have a nutritive value similar to other dark green leaves and are an extremely valuable source of vitamins A (carotene) and C, iron, calcium and protein (Latham, 1979).
Despite these limitations, the medical literature represents a large and extremely valuable source of information from hundreds of incidents that together should inform future practice.
While Facebook shouldn't be your only source of traffic (not by a long shot), it can be an extremely valuable and predictable source of leads when used right.
This feature makes these stem cells an extremely valuable and potent cell source.
Extrafloral nectar is like an energy drink for ants, because it is a source of carbohydrates and amino acids (Davidson 1997; Petanidou et al. 2006), and water represents an extremely valuable resource especially in deserts (Ruffner and Clark 1986).
Trump has made an extremely valuable discovery.
