The series is arranged chronologically beginning in 1881. There is a single folder of outgoing correspondence for 1887 to 1890. The remainder of the series is all incoming correspondence dating through 1934. The bulk of the letters are from suppliers of mining goods and services. The letters range from national suppliers of sophisticated mining equipment like Fraser and Chalmers to local suppliers of hay for company stables. Many of the letters merely solicit business from the mining companies, attempting to sell everything from flint pebbles for ore processing to the services of a zither player. The letters from suppliers include information on the whole range of materials required by the two companies and the national scope of the mining business. Many of the letters concern the costs of supplies and the difficulty of shipping material to Marysville. The letters also relate to unpaid bills, mine injuries, job inquiries, and the personal matters of various managers. There are letters regarding other mining properties, price quotations, clippings from the , and mining prospects at the Drumlummon. There are several items of particular interest in this series. The communications between the London headquarters of the Montana Mining Company and Marysville are generally in telegraphic code for secrecy. There are numerous code sheets to help company officials decode the messages. in Series VII also relates to this material. The correspondence relating to both companies also overlaps chronologically. Letters relating to the St. Louis Mining and Milling Company appear in the files nearly 20 years before they own the Drumlummon. There is also a report from a Pinkerton detective investigating union activity in Marysville and Butte. The series provides insight into the international nature of mining in Montana. The letters also detail the logistical and financial difficulties of running a mine.

This brief series contains material relating to the Montana Mining Company's insurance subsidiary. The Association was limited to employees of the Montana Mining Company. The Board of Trustees was composed of two members elected by employees and two members appointed by the Company. The series includes a copy of the by-laws, rules, and regulations of the Association from 1900. The remainder of the series consists of the canceled checks of the Insurance Association dating from 1888 to 1897. These provide insight into the costs of running the Insurance Association and include both claims paid to workers and materials for administration.

This series is broken into several categories and arranged chronologically within each category. The categories within the series are arranged alphabetically. The series contains materials housed in traditional folders and a significant number of oversize materials. These are housed in oversize boxes and map cases. The bulk of this series is comprised of assay reports, bullion returns, and mill reports. However, there are folders for assets and liabilities, federal reports, insurance, invoices, mine progress reports, claim descriptions and names, payroll records, reports on other mines, and tax assessments. The materials in the series provide a solid background for understanding the finances of the Drumlummon mine and the two companies that owned it. The assay reports present a fairly complete picture of the ore values for the early years of the mine. The quantity of reports declines sharply after 1902 and is sporadic for the ensuing years. The bullion returns document the metal bars produced after smelting. These returns are less complete than the assay returns. They are intermittent for the entire history of the mine, although the period around 1900 is reasonably complete. Mill reports concern the quantity of the ore processed at each of the stamp mills that the companies operated. They also contain information concerning the quantity of pulp and tailings each produced and the values of the ore being processed. These reports are very complete through the early 1890's and include a set of blueprints for a 1913 mill. There are reports on several other mines in British Columbia, the Lucky Girl in Tuscarora, Nevada, and the Silver Bell in Montana. The Lucky Girl was owned by the Montana Mining Company and the reports include most financial aspects of the operations over eight years. The payroll records and invoices for the Drumlummon are incomplete but provide insight into the costs of running a mine. They also include crucial information about workers and the division of labor in the mines. The information on expenses and assets is very useful for understanding the difficulties of financing mining. The information is particularly detailed for the era between 1883 and 1907. There are detailed descriptions of the costs of individual shafts, mills, and payroll. The order books contain detailed records for all the goods required for the years from 1887 to 1897 and the orders for the Rose Densmore mine for 1890. The delivery book contains information for goods delivered from 1889 to 1897. There are folders containing information on tax assessments of the mines from 1888 to 1933 and the Federal Census of Mines for 1926 to 1933. There are a few insurance documents relating to death benefits for a miner and a fire insurance policy from 1913. There are also reports of equipment for the Marysville Electric Light and Water Company.

This series contains materials related to the governance of both the Montana Mining Company and the St. Louis Mining and Milling Company. The material is primarily focused on official company correspondence, decisions, and records. The bulk of material is concentrated in the period from 1911 to 1933 and the control of the Drumlummon by the St. Louis Mining and Milling Company. The information includes reports from the Board of Directors, cable reports from the Montana Mining Company, mining reports from outside experts, mine superintendent reports, and the letters and reports of the corporate officers of the St. Louis Mining and Milling Company. Bondholder and Stockholder records and letters represent the majority of the material in the series. The divisive struggles that plagued the mine after the St. Louis Mining and Milling Company took control of the property are clearly documented here. The fight to raise money for mine improvements and to fend off bankruptcy can be traced in the letters and reports. These letters and reports contain requests for share assessments, candid evaluations of the company's financial situation, and accusations of mismanagement from various stockholder factions. The reports from the secretary of the Montana Company are generally quarterly earnings statements, although there are some monthly returns and some changes in share volume and working capital. Most of the officers' material from the St. Louis Mining and Milling Company is also related to the financial struggles of the company beginning in 1908. The bulk of these folders contain letters to stockholders asking for money, assessing shares, or reporting on the desperate financial straits of the corporation. The reports from outside mining experts candidly assess the mineral and financial opportunities available at the Drumlummon mine at two significant points in the mine's history. The first round of reports is from 1882 to 1885 and was used by the Montana Mining Company to judge the value of the property prior to their initial purchase of the mine from Thomas Cruse. The second report is from Harry Quinby criticizing the management of the mine by St. Louis Mining and Milling superintendent William Mayger in 1912. The superintendents' reports span nearly the entire life of the Drumlummon from 1885 to 1929. They provide insight into the more routine workings of the mine and the breadth of expertise required of a mine manager. These reports also provide a more intimate overview of the workings of the mines than the reports of the company officers. The series is rounded out by cable reports to the London headquarters of the Montana Mining Company from 1886 to 1901 and a number of unidentified mine reports.

This series contains material relating to the legal affairs of both the Montana Mining Company and the St. Louis Mining and Milling Company. The series is arranged chronologically with materials grouped in folders according to years. The series begins with a Marysville mining claim from 1875 which is housed in an oversize box. The bulk of the remaining material relates to the apex litigation between the St. Louis Mining and Milling Company and the Montana Mining Company beginning in 1890 and continuing until the settlement of the suit in 1911. The majority of documents from the case are legal briefs but there also legal decisions, summons, injunctions, and sheriff's deeds. The papers provide insight into the bitter legal battle for control of the mining ground in question. This struggle resulted in the eventual victory of the St. Louis Mining and Milling Company and the sale of the Montana Mining Company's property at sheriff's sale in 1911. There are also briefs and other documents relating to litigation between the St. Louis Mining and Milling Company and a number of suppliers and employees. The documents in the series after 1911 relate to the struggle for control of the St. Louis Mining and Milling Company. The resulting fight to keep the Drumlummon open was waged among stock and bondholders and in court from 1911 to the closing of the mines in the 1930's. The remainder of the series is rounded out by attorney's bills, garnishment of wages, leases, settlements with injured workers, and an undated brief from the U.S. Circuit Court of Appeals.

This small series contains a smattering of printed materials. There are newspaper clippings from Helena and Butte newspapers from 1924 to 1989. The majority of the articles pertain to attempts at re-opening the Drumlummon mine. There is a folder containing undated signs relating to safety and worker's compensation in the mine. A copy of from 1870 is included here and is useful in deciphering some of the coded telegrams sent from Marysville to the London headquarters of the Montana Mining Company. There are reports of the Montana Society of Civil Engineers from 1897. These include meeting summaries and a list of all Society members in February 1897. Finally there are printed materials with the headings of the Montana Mining Company and the Drumlummon Provident and Accident Insurance Association. These include unused envelopes, stationery, labor use reporting sheets for the mine and mills, and order forms.